Objectives Smoke-free policies not only reduce harm to non-smokers, they may also reduce harm to smokers by decreasing the number of cigarettes smoked and increasing the likelihood of a successful quit attempt. However, little is known about the impact of exposure to smoking on patios on smoking behaviour.

Design and participants Smokers from the Ontario Tobacco Survey, a longitudinal population representative cohort of smokers (2005–2011). There were 3460 current smokers who had completed one to six follow-ups and were asked at each follow-up whether or not they had been exposed to smoking on patios in the month.

Main outcome measures Generalised estimating equations and survival analysis were used to examine the association between exposure to patio smoking and smoking behaviour changes (making a quit attempt and time to relapse after a quit attempt), controlling for potential confounders.

Results Smokers who were exposed to smoking on patios (adjusted incident rate ratio (aIRR) = 0.89; 95% CI 0.81 to 0.97) or had been to a patio (aIRR = 0.86; 95% CI 0.74 to 0.99) were less likely to have made a quit attempt than smokers who had not visited a patio. Smokers who were exposed to smoking on patios were more likely to relapse (adjusted HR=2.40; 95% CI 1.07 to 5.40)) after making a quit attempt than those who visited a patio but were not exposed to smoking.

Conclusions Exposure to smoking on patios of a bar or restaurant is associated with a lower likelihood of success in a quit attempt. Instituting smoke-free patio regulations may help smokers avoid relapse after quitting.