This paper uses the widespread variation across states in the timing of adoption of tougher drunk driving laws that set very low legal blood alcohol limits for drivers under age 21-“zero tolerance” (ZT) laws-to provide new evidence on the causal effect of alcohol use on youth suicide. ZT laws reduced heavy episodic drinking by underage men, with no effect for slightly older males. I estimate the reduced form effect of ZT policy adoption on suicide deaths among 15-17-, 18-20-, 21-24-, and 25-29-year-old males and females for the period 1981-1998. The models control for macroeconomic conditions, demographic changes, other alcohol control policies, state and year fixed effects, and smooth state trends. Results indicate statistically significant reductions in suicide among young males aged 15-17 and 18-20 associated with adoption of ZT laws on the order of 7 to 10 percent. I find no effects for slightly older males who were unaffected by the tougher drunk driving laws, and no consistent effects for females. These results provide new and compelling evidence that heavy alcohol use causes young male suicide. Â© 2004 by the Association for Public Policy Analysis and Management.