DOI: http://dx.doi.org/10.5007/1980-0037.2017v19n2p174 The aim of this study was to analyze the contribution of physical activity (PA) and sedentary time (ST) to Body Mass Index (BMI) in adults. The study was conducted in 2009, in Curitiba, Parana, Brazil with adults aged 18-65 years (1,411). A multidimensional questionnaire was used in which BMI, weekly minutes of PA and ST were obtained from self-reports. PA and ST were combined to determine the following independent variables: a) “active and not sedentary”; b) “active and sedentary”; c) “not active and not sedentary” and d) “not active and sedentary”. Multinomial logistic regressions were used to test the associations between PA, ST and BMI. The adjusted regression model showed that PA, regardless of ST, lowered the likelihood of participants being classified as obese by 34% and 55%, respectively. In addition, PA at recommended levels (≥150 minutes/week), while not being sedentary, lowered by 85% the likelihood of being classified in the underweight category. Finally, ≥10 minutes/week of PA, while reporting higher ST levels, reduced the likelihood of being classified as overweight by 37%. PA is associated with BMI regardless of TS. In addition, PA at recommended levels is inversely related to obesity and overweight.