Some researchers are promoting the use of smokeless tobacco as safer than cigarette smoking and as a possible method for quitting smoking, but smokeless tobacco might be a gateway drug that leads to smoking, and the availability and marketing of smokeless tobacco may keep smokers from quitting. This study assessed 4-year initiation rates of smokeless tobacco use and cigarette smoking in relation to each other and examined switching between the products. Data were from the 1989 Teenage Attitudes and Practices Survey and its 1993 follow-up study, comprising a nationally representative U.S. cohort of 7,960 people aged 11–19 years at baseline. Analyses were limited to males with complete data on smoking and smokeless tobacco use at both interviews ( n =3,996). Young males who were not smokers in 1989 but regularly used smokeless tobacco were more than three times as likely as never users to be current smokers 4 years later (23.9% vs. 7.6%), adjusted OR =3.45 (95% CI =1.84–6.47). In contrast, 2.4% of current smokers and 1.5% of never smokers at baseline became current regular smokeless tobacco users by follow-up. More than 80% of baseline current smokers were still smokers 4 years later, and more than 40% of baseline current regular smokeless tobacco users became smokers either in addition to or in place of smokeless tobacco use. It appears that smokeless tobacco may be a starter product for subsequent smoking among young U.S. males but may have little effect on quitting smoking.