Background: It is unknown if nutritional status could influence the accuracy of self-reported physical activity (PA) levels. Aim: To compare PA measured using the international physical activity questionnaire (IPAQ) and by accelerometry (ActiGraph) according to nutritional status in Chilean adults. Material and Methods: This is an observational cross-sectional study that used information from the GENADIO project carried out in Chile between 2009-2011. The sample consisted of 322 people. PA levels and sitting time were determined through the IPAQ self-report questionnaire and ActiGraph accelerometers (GTM1). The nutritional status was determined according to body mass index (BMI). Results: Compared with the measurement made with accelerometry, the IPAQ self-report questionnaire underestimated the levels of light PA, total PA and sedentary time in -171.5, -54.8 and -40.6 min / day, respectively. However, IPAQ overestimated the levels of moderate PA and vigorous PA in 91.0 and 47.3 min/day respectively, compared with accelerometry. Compared with normal weight, obese subjects reported higher levels of moderate PA (105.5 and 48.9 min/day, respectively) and vigorous PA (54.1 and 38.3 min/day respectively). Total PA had a greater delta of underestimation between IPAQ and accelerometer measurements in normal weight than in obese subjects (-122.1 vs -16.5 min/day, respectively). Conclusions: The measurement of PA by means of a self-report questionnaire was discrepant with its objective measurement with an accelerometer. The discrepancy is even higher in obese people.