OBJECTIVE: to analyze the relationship between body image, body weight and physical activity among young adults in the city of Ribeirão Preto (SP). METHOD: a cohort study of individuals born between 1978-1979, classified by sex, education level, body mass index and physical activity level assessed by the International Physical Activity Questionnaire (IPAQ). RESULTS: 2035 individuals had been evaluated, (51.8% female) of whom 1727 (84.8%) reported having studied over nine years. Both the mean weight (77.6 ± 15 kg) and body mass index (25 ± 4.4 kg/m²) were higher for males. Regarding the classification of body awareness, 81.6% of women overestimated their body weight and 78.2% of men underestimated. Among all individuals who underestimate their body weight, 92.3% had schooling of more than nine years. Individuals who overestimated their weight were the least developed physical activity (58.6%). In groups of individuals who considered the appropriate weight or overestimated, 48.3% and 51.2%, respectively, were classified as active or very active. CONCLUSION: body mass index and physical activity have contributed to better evaluation of their own weight, whereas female gender and higher educational level had a direct relationship with the distortion of perception, with a tendency to overestimate their own weight.