Studies of worksite smoking bans often find that they fail to increase the rate of smoking cessation. To see whether duration of exposure to restrictive policies was an important element, we surveyed workers by phone to examine the effect of being continuously employed at a smokefree worksite for 3 years. Results showed that worksite policy was unrelated to smoking cessation. However, 12% of respondents at smokefree worksites reported that smoking had taken place in their work area, and over 20% reported at least 2 hours of worksite environmental tobacco smoke (ETS) exposure during the prior week. When minimal ETS exposure is used as an indicator of an effectively enforced smoking ban, logistic regression demonstrates that continuous employment at such a worksite strongly predicts smoking cessation. Failure to demonstrate a significant impact of worksite smoking bans on cessation in this and other studies may be due to poor enforcement of smoking policies.