diff --git a/usr.bin/truss/alpha-fbsd.c b/usr.bin/truss/alpha-fbsd.c
index 4a88ff1d94b5..a7b5baf12443 100644
--- a/usr.bin/truss/alpha-fbsd.c
+++ b/usr.bin/truss/alpha-fbsd.c
@@ -155,6 +155,14 @@ alpha_syscall_entry(struct trussinfo *trussinfo, int nargs) {
     fprintf(trussinfo->outfile, "-- UNKNOWN SYSCALL %d --\n", syscall);
   }
 
+  if (fsc.name && (trussinfo->flags & FOLLOWFORKS)
+   && ((!strcmp(fsc.name, "fork")
+    || !strcmp(fsc.name, "rfork")
+    || !strcmp(fsc.name, "vfork"))))
+  {
+    trussinfo->in_fork = 1;
+  }
+
   if (nargs == 0)
     return;
 
diff --git a/usr.bin/truss/amd64-fbsd32.c b/usr.bin/truss/amd64-fbsd32.c
index 702db80213f3..6364927ca620 100644
--- a/usr.bin/truss/amd64-fbsd32.c
+++ b/usr.bin/truss/amd64-fbsd32.c
@@ -160,6 +160,14 @@ i386_syscall_entry(struct trussinfo *trussinfo, int nargs) {
     fprintf(trussinfo->outfile, "-- UNKNOWN SYSCALL %d --\n", syscall);
   }
 
+  if (fsc.name && (trussinfo->flags & FOLLOWFORKS)
+   && ((!strcmp(fsc.name, "fork")
+    || !strcmp(fsc.name, "rfork")
+    || !strcmp(fsc.name, "vfork"))))
+  {
+    trussinfo->in_fork = 1;
+  }
+
   if (nargs == 0)
     return;
 
diff --git a/usr.bin/truss/amd64-linux32.c b/usr.bin/truss/amd64-linux32.c
index e6a560a34a4e..f307c8017307 100644
--- a/usr.bin/truss/amd64-linux32.c
+++ b/usr.bin/truss/amd64-linux32.c
@@ -120,6 +120,13 @@ i386_linux_syscall_entry(struct trussinfo *trussinfo, int nargs) {
     fprintf(trussinfo->outfile, "-- UNKNOWN SYSCALL %d\n", syscall);
   }
 
+  if (lsc.name && (trussinfo->flags & FOLLOWFORKS)
+   && ((!strcmp(lsc.name, "linux_fork")
+    || !strcmp(lsc.name, "linux_vfork"))))
+  {
+    trussinfo->in_fork = 1;
+  }
+
   if (nargs == 0)
     return;
 
diff --git a/usr.bin/truss/extern.h b/usr.bin/truss/extern.h
index ea7c435521b3..a708dda1b490 100644
--- a/usr.bin/truss/extern.h
+++ b/usr.bin/truss/extern.h
@@ -32,7 +32,7 @@
  */
 
 extern int setup_and_wait(char **);
-extern int start_tracing(int, int);
+extern int start_tracing(int, int, int);
 extern void restore_proc(int);
 extern const char *ioctlname(register_t val);
 #ifdef __alpha__
diff --git a/usr.bin/truss/i386-fbsd.c b/usr.bin/truss/i386-fbsd.c
index 702db80213f3..6364927ca620 100644
--- a/usr.bin/truss/i386-fbsd.c
+++ b/usr.bin/truss/i386-fbsd.c
@@ -160,6 +160,14 @@ i386_syscall_entry(struct trussinfo *trussinfo, int nargs) {
     fprintf(trussinfo->outfile, "-- UNKNOWN SYSCALL %d --\n", syscall);
   }
 
+  if (fsc.name && (trussinfo->flags & FOLLOWFORKS)
+   && ((!strcmp(fsc.name, "fork")
+    || !strcmp(fsc.name, "rfork")
+    || !strcmp(fsc.name, "vfork"))))
+  {
+    trussinfo->in_fork = 1;
+  }
+
   if (nargs == 0)
     return;
 
diff --git a/usr.bin/truss/i386-linux.c b/usr.bin/truss/i386-linux.c
index e6a560a34a4e..f307c8017307 100644
--- a/usr.bin/truss/i386-linux.c
+++ b/usr.bin/truss/i386-linux.c
@@ -120,6 +120,13 @@ i386_linux_syscall_entry(struct trussinfo *trussinfo, int nargs) {
     fprintf(trussinfo->outfile, "-- UNKNOWN SYSCALL %d\n", syscall);
   }
 
+  if (lsc.name && (trussinfo->flags & FOLLOWFORKS)
+   && ((!strcmp(lsc.name, "linux_fork")
+    || !strcmp(lsc.name, "linux_vfork"))))
+  {
+    trussinfo->in_fork = 1;
+  }
+
   if (nargs == 0)
     return;
 
diff --git a/usr.bin/truss/main.c b/usr.bin/truss/main.c
index 503329ffc93e..d1a236a7992a 100644
--- a/usr.bin/truss/main.c
+++ b/usr.bin/truss/main.c
@@ -67,8 +67,8 @@ static __inline void
 usage(void)
 {
   fprintf(stderr, "%s\n%s\n",
-	"usage: truss [-S] [-o file] -p pid",
-	"       truss [-S] [-o file] command [args]");
+	"usage: truss [-fS] [-o file] -p pid",
+	"       truss [-fS] [-o file] command [args]");
   exit(1);
 }
 
@@ -145,11 +145,14 @@ main(int ac, char **av) {
   bzero(trussinfo, sizeof(struct trussinfo));
   trussinfo->outfile = stderr;
 
-  while ((c = getopt(ac, av, "p:o:S")) != -1) {
+  while ((c = getopt(ac, av, "p:o:fS")) != -1) {
     switch (c) {
     case 'p':	/* specified pid */
       trussinfo->pid = atoi(optarg);
       break;
+    case 'f': /* Follow fork()'s */
+      trussinfo->flags |= FOLLOWFORKS;
+      break;
     case 'o':	/* Specified output file */
       fname = optarg;
       break;
@@ -195,9 +198,11 @@ main(int ac, char **av) {
    * be woken up, either in exit() or in execve().
    */
 
+START_TRACE:
   Procfd = start_tracing(
 		trussinfo->pid, S_EXEC | S_SCE | S_SCX | S_CORE | S_EXIT |
-		((trussinfo->flags & NOSIGS) ? 0 : S_SIG));
+		((trussinfo->flags & NOSIGS) ? 0 : S_SIG),
+		((trussinfo->flags & FOLLOWFORKS) ? PF_FORK : 0));
   if (Procfd == -1)
     return 0;
 
@@ -232,6 +237,23 @@ main(int ac, char **av) {
 	  in_exec = 0;
 	  break;
 	}
+
+	if (trussinfo->in_fork && (trussinfo->flags & FOLLOWFORKS)) {
+	  int childpid;
+
+	  trussinfo->in_fork = 0;
+	  childpid = funcs->exit_syscall(trussinfo, pfs.val);
+
+	  /*
+	   * Fork a new copy of ourself to trace the child of the
+	   * original traced process.
+	   */
+	  if (fork() == 0) {
+	    trussinfo->pid = childpid;
+	    goto START_TRACE;
+	  }
+	  break;
+	}
 	funcs->exit_syscall(trussinfo, pfs.val);
 	break;
       case S_SIG:
diff --git a/usr.bin/truss/setup.c b/usr.bin/truss/setup.c
index baeb570af403..e3d52a4e5e93 100644
--- a/usr.bin/truss/setup.c
+++ b/usr.bin/truss/setup.c
@@ -130,7 +130,7 @@ setup_and_wait(char *command[]) {
  */
 
 int
-start_tracing(int pid, int flags) {
+start_tracing(int pid, int eventflags, int flags) {
   int fd;
   char buf[32];
   struct procfs_status tmp;
@@ -153,7 +153,7 @@ start_tracing(int pid, int flags) {
   }
   evflags = tmp.events;
 
-  if (ioctl(fd, PIOCBIS, flags) == -1)
+  if (ioctl(fd, PIOCBIS, eventflags) == -1)
     err(9, "cannot set procfs event bit mask");
 
   /*
@@ -162,7 +162,7 @@ start_tracing(int pid, int flags) {
    * needs to be woken up via procctl.
    */
 
-  if (ioctl(fd, PIOCSFL, 0) == -1)
+  if (ioctl(fd, PIOCSFL, flags) == -1)
     warn("cannot clear PF_LINGER");
 
   return fd;
diff --git a/usr.bin/truss/syscalls.c b/usr.bin/truss/syscalls.c
index 432197fd89e1..8056aa122270 100644
--- a/usr.bin/truss/syscalls.c
+++ b/usr.bin/truss/syscalls.c
@@ -357,7 +357,12 @@ void
 print_syscall(struct trussinfo *trussinfo, const char *name, int nargs, char **s_args) {
   int i;
   int len = 0;
+
+  if (trussinfo->flags & FOLLOWFORKS)
+    len += fprintf(trussinfo->outfile, "%5d:  ", trussinfo->pid);
+
   len += fprintf(trussinfo->outfile, "%s(", name);
+
   for (i = 0; i < nargs; i++) {
     if (s_args[i])
       len += fprintf(trussinfo->outfile, "%s", s_args[i]);
diff --git a/usr.bin/truss/truss.1 b/usr.bin/truss/truss.1
index f2a99cc79c03..58f9ac53d820 100644
--- a/usr.bin/truss/truss.1
+++ b/usr.bin/truss/truss.1
@@ -8,11 +8,11 @@
 .Nd trace system calls
 .Sh SYNOPSIS
 .Nm
-.Op Fl S
+.Op Fl fS
 .Op Fl o Ar file
 .Fl p Ar pid
 .Nm
-.Op Fl S
+.Op Fl fS
 .Op Fl o Ar file
 command
 .Op args
@@ -26,6 +26,9 @@ It does this by stopping and restarting the process being monitored via
 .Pp
 The options are as follows:
 .Bl -tag -width indent
+.It Fl f
+Trace decendants of the original traced process created by fork(),
+vfork, etc.
 .It Fl S
 Do not display information about signals received by the process.
 (Normally,
diff --git a/usr.bin/truss/truss.h b/usr.bin/truss/truss.h
index 24396ad301e1..f77202aec264 100644
--- a/usr.bin/truss/truss.h
+++ b/usr.bin/truss/truss.h
@@ -25,11 +25,13 @@
  * $FreeBSD$
  */
 
+#define FOLLOWFORKS        0x00000001
 #define NOSIGS             0x00000008
 
 struct trussinfo
 {
 	int pid;
 	int flags;
+	int in_fork;
 	FILE *outfile;
 };