Background and Objectives: Approximately one in five ex-smokers reduces or maintains weight after smoking cessation but little is known about who succeeds to avoid weight gain. The purpose of this study was to identify predictors of weight reduction after long-term smoking cessation in a general population. Methods: Data was obtained from two Danish population-based cohorts (the Inter99 and the Helbred2006 study). Anthropometric measurements were performed by trained research staff. Out of 3.577 daily smokers at baseline 317 participants had quit smoking at the five-year follow-up for at least one year. Multiple logistic regression analysis was performed to determine predictors of weight reduction. Results: Thirteen percent reduced weight by at least 1 kg and 4% maintained their weight. Quitters with obesity had more than seven times higher odds than normal weight quitters to lose weight (OR 7.13 (95% CI 2.76–19.71)), and they had the largest median weight loss of 4.45 kg. The only other significant predictor of weight reduction was low tobacco consumption at baseline. Conclusions: Predictors of weight reduction after smoking cessation were high body mass index and low tobacco consumption at baseline. This study might motivate smokers with obesity to quit smoking and health professionals to give them support.