New research suggests a surprising number of teenagers -- nearly 15 percent -- think they're going to die young, leading many to drug use, suicide attempts and other unsafe behavior.

The study challenges conventional wisdom that says teens engage in risky behavior because they think they're invulnerable to harm. Instead, study author Dr. Iris Borowsky of the University of Minnesota says a sizable number of teens may take chances "because they feel hopeless and figure that not much is at stake."

Such behavior threatens to turn their fatalism into a self-fulfilling prophecy. Over seven years, kids who thought they would die early were seven times more likely than optimistic kids to be subsequently diagnosed with AIDS. They also were more likely to attempt suicide and get in fights resulting in serious injuries.

The study appears in the July issue of Pediatrics.