OBJECTIVES: To characterize how physical activity and sedentary behavior have been measured in national health surveys in South American countries. METHODS: An extensive search was made for national health surveys from all 12 South American countries through health websites, national statistical offices, and contact with researchers and policy-makers. The following eligibility criteria were used to select surveys: conducted in a South American country; used a nationally representative sample ≥ 18 years; coordinated by the public, private or mixed private-public sector; and assessed physical activity and/or sedentary behavior. Data were extracted on general information about the surveys, specific details about the physical activity and sedentary behavior assessment, and additional questions related to activity behavior. RESULTS: In total, 36 surveys were included, two of which were multicountry surveys; all surveys assessed physical activity and 27 assessed sedentary behavior. Most surveys (23/36; 64%) were based on previously validated international questionnaires, but 13 (57%) of these deviated from the reference tools, introducing changes and adaptations. Sedentary behavior was assessed mostly through questions on screen time and/or daily sitting time in the same physical activity questionnaires. No survey used device-based measures to generate data on these behaviors. CONCLUSIONS: Differences between instruments used and modifications limit the comparability of data across countries. This highlights the importance of standardizing assessment within South America for physical activity and sedentary behavior sections in national surveys, with the broader aim of contributing to establishing a standardized strategy for the surveillance of physical activity and sedentary behavior in South America.