As others have said, those were common in the '80s. I had one on my first mountain bike, a Mongoose I got in '83 or '84. They work fine; if it's in good shape there's no reason to worry about it.
One thing to watch if you do replace: a lot of those, including mine, were an old-school diameter, I think .833 inch, that had been the American standard on kids' bikes and cruisers. The industry was just starting the move to what were called "one-inch stems" (actually 22.2mm, while an inch is 25.4mm. And just to complicate things, French bikes' stems were 22.0, just enough difference to they didn't interchange with either of the others). One-inch stems are still fairly easy to find, but if you have one of the .833s, good luck...