This study assessed the effects of New York State's recently adopted mandatory seat belt use law on teenage drivers. Teenage drivers were observed as they entered high school parking lots before the law was adopted, after it was adopted but before it was effective, one month after the effective date, and again five months after the effective date. The results showed that 14% of the teenage drivers were wearing either shoulder or lap belts or both prior to adoption of the law. This increased to 22% after adoption of the law, 60% one month after the effective date of the law, and 63% five months after the effective date. Teenagers using seat belts were more often female, were younger, had completed driver education and had a longer trip from home to school. Both before and after the law, teenage belt use was similar to, but typically lower than, belt use in the community in which the school was located.