Alt's first big break in modeling in 1980, when she was featured on the cover of Harper's Bazaar magazine, but she gained real fame in 1982 when she was featured on the cover of the Sports Illustrated Swimsuit Issue. During the 1980's she appeared on over 500 magazine covers, becoming one the most famous models of her era. Alt was referred to as "The Face" by Life Magazine. During the height of her popularity, she was the face of ad campaigns for Diet Pepsi, General Motors, Cover Girl Cosmetics, Noxema, Hanes and numerous others. She was the first model to produce her own posters and calendars. As the eighties were winding down, Alt very publicly abandoned the fashion industry in favor of acting, which she said was her passion.

Since 1986 she has been in a variety of movies. Most were Italian, but one of her recent starring roles was in the Canadian movie Snakehead Terror. She played "Karen Oldham" in the TV adaptation of Peter Benchley's "Amazon" (1999). Her TV guest appearan