9032 Background: Smoking during cancer treatment negatively impacts treatment, survival and quality of life. Lung cancer patients with a smoking history often continue to smoke; some ex-smokers re-start after diagnosis. Social environment impacts cessation and recidivism rates in non-cancer patients. We assessed whether the same influences occur among lung cancer patients. Methods: Lung cancer patients, recruited from Princess Margaret Hospital, completed a baseline questionnaire about their demographics and smoking history (at diagnosis). A follow-up questionnaire was administered at a median of two years, assessing changes in smoking habits, exposure at home/work/among friends, healthcare use, social support and alcohol use since diagnosis. The relationship between each variable with cessation/recidivism was analyzed. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated. Results: 478 patients completed both questionnaires. Of the 100 current smokers at diagnosis; 52 quit by the time of the follow-up questionnaire. Among 294 ex-smokers, 15 started to smoke after diagnosis. None of the 84 never smokers at baseline started to smoke after diagnosis. Exposure to smoking at home was associated with continued smoking and relapse (OR=5.1, 95% CI: 1.8–14.3, p=0.001; and OR=3.9, 95% CI: 0.8–14.4, p=0.04, respectively). Specifically, spousal smoking was associated with both continued smoking (OR=7.3, 95% CI: 2.4–21.7, p=2.0E-04) and recidivism (OR=3.7, 95% CI: 0.6–16.6, p=0.08). Having more than a few friends who smoke is associated with continued smoking (OR=3.5, 95% CI: 1.4–8.7, p=0.005) and relapse (OR=4.8, 95% CI: 1.5–15.0, p=0.004). Not completing high school was also associated with continued smoking (OR=3.0, 95% CI: 1.2–7.6, p=0.02). Multivariate analysis identified spousal smoking as the major single predictor of continued smoking (OR=8.8, 95% CI: 2.2–34.8, p=0.002). Conclusions: Smoking cessation programs for lung cancer patients should not only target the patient but also include the immediate family, consider a patient’s peers and be tailored to the patient’s education level. Involvement of the immediate family and consideration of peers may help prevent smoking relapse.