This study assessed the comparability and reliability of paper-based and computer-based administration of psychosocial construct measures related to adolescents engaging in physical activity and sedentary behaviors. Adolescents (n = 76; 55% girls, 49% Hispanic, 18% non-Hispanic-white; M age = 13 years) completed measures of behavior change strategies, self-efficacy, decisional balance, family and peer influences, enjoyment, activity choices, and environmental influences. Overall, the adolescents provided equivalent responses on paper and computer formats. Reliability estimates were generally good for the multiple-item constructs, but single-item measures tended to demonstrate low reliability. Average scale internal consistency was significantly higher for measures administered with the computer format compared to the paper format, but test-rest reliability estimates were not significantly different between formats.