Concern about weight gain is a barrier to smoking-cessation, but determinants of postcessation weight-concern have not been comprehensively assessed in the context of community-based cessation programs. This cross-sectional analysis used baseline data from a cessation trial of 392 adults randomized to physical activity (PA) or general wellness counseling as adjunctive treatment for smoking. Outcomes were 1) smoking behaviors to control weight and 2) anticipating relapse due to weight gain. Independent variables were PA and perceptions, sociodemographics, psychosocial measures, smoking behavior and perceptions, diet, and BMI. From bivariable models examining main and sex interaction effects, significant variables were entered into a linear (control) or logistic (relapse) regression model to identify key determinants. For both measures, weight-concern was greater (p < .05) for female smokers (standardized b = 0.52, SE = 0.10; OR = 0.29, 95 % CI = 0.17-0.49), White (b = 0.12, SE = 0.05; OR = 0.39, 95 % CI = 0.23-0.66), and less motivated to quit (b = -0.14, SE = 0.05; OR = 0.77, 95 % CI = 0.59-1.0). Higher scores for smoking to control weight were associated with less PA (b = -0.10, SE = 0.05) and higher BMI (b = 0.21, SE = 0.05). For men, higher BMI was associated with greater anticipation of relapse (OR = 2.54, 95 % CI = 1.42-4.56). Among adults attempting cessation, women, White smokers, and those less motivated to quit were more likely to smoke for weight control and to relapse due to weight gain. Higher BMI was associated with greater anticipation of relapse for men, but not women. Weight-concerns, for both measures, were not related to smoking history, psychosocial functioning, PA engagement or attitudes, or dietary variables. Results suggest potential cessation intervention targets for weight-concerned smokers.