ABSTRACT Objective: To evaluate weight changes after 12 months of biochemically confirmed smoking abstinence, comparing patients who lost weight or maintained their baseline weight with those who gained weight. Methods: This was a real-world prospective cohort study conducted at the Outpatient Smoking Cessation Clinic of São Lucas Hospital, in the city of Porto Alegre, Brazil, between 2010 and 2016. The patients evaluated received intensive smoking cessation counseling, focused especially on weight issues, together with pharmacotherapy, and were followed for 12 months. The baseline and final weights were measured. Continuous abstinence was confirmed by determining the concentration of exhaled carbon monoxide (eCO). Results: Of a total of 348 patients evaluated, 161 (46.2%) achieved continuous abstinence (eCO < 10 ppm) over the 12-month follow-up period. Of those 161 patients, 104 (64.6%) maintained their initial weight or had a weight change of no more than 5% in relation to their baseline weight, whereas the remaining 57 (35.4%) had a weight gain of more than 5%, 18 of those patients showing a > 10% increase over their baseline weight. The number needed to harm (i.e., the number of patients required in order to detect one patient with a weight increase) was calculated to be 3.6 (95% CI: 2.8-5.4). Conclusions: Weight gain is not necessarily associated with smoking cessation, and smokers who are motivated to quit should be informed of that fact. This information could also be useful for addressing smokers who are still undecided because of possibility of weight gain.