diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -225,24 +225,25 @@
    Exit from Python.  This is implemented by raising the :exc:`SystemExit`
    exception, so cleanup actions specified by finally clauses of :keyword:`try`
    statements are honored, and it is possible to intercept the exit attempt at
-   an outer level.
+   an outer level. When called from a thread other than the main thread, this
+   is equivalent to calling :func:`thread.exit` and causes the thread to exit
+   silently.

    The optional argument *arg* can be an integer giving the exit status
-   (defaulting to zero), or another type of object.  If it is an integer, zero
-   is considered "successful termination" and any nonzero value is considered
-   "abnormal termination" by shells and the like.  Most systems require it to be
-   in the range 0-127, and produce undefined results otherwise.  Some systems
-   have a convention for assigning specific meanings to specific exit codes, but
-   these are generally underdeveloped; Unix programs generally use 2 for command
-   line syntax errors and 1 for all other kind of errors.  If another type of
-   object is passed, ``None`` is equivalent to passing zero, and any other
-   object is printed to :data:`stderr` and results in an exit code of 1.  In
-   particular, ``sys.exit("some error message")`` is a quick way to exit a
-   program when an error occurs.
+   (defaulting to zero), or another type of object. Passing ``None`` is
+   equivalent to passing zero. Any other object is printed to :data:`stderr`
+   and results in an exit status of 1.  In particular,
+   ``sys.exit("some error message")`` is a quick way to exit a program when an
+   error occurs. When called from a thread other than the main thread, nothing
+   is printed and the argument is ignored.

-   Since :func:`exit` ultimately "only" raises an exception, it will only exit
-   the process when called from the main thread, and the exception is not
-   intercepted.
+   An exit status of zero is considered “successful termination” and any
+   nonzero status is considered "abnormal termination" by shells and the like.
+   Most systems require it to be in the range 0-127, and produce undefined
+   results otherwise.  Some systems have a convention for assigning specific
+   meanings to specific exit codes, but these are generally underdeveloped;
+   Unix programs generally use 2 for command line syntax errors and 1 for all
+   other kind of errors.


 .. data:: exitfunc