The purpose of this study was to examine the convergent validity and test-retest reliability of the Oxford Physical Activity Questionnaire (OPAQ), a self-administered questionnaire designed to assess the activity patterns of adolescents. The test-retest reliability of the OPAQ was assessed by administering the questionnaire on two occasions separated by 1 week (N = 87, mean age = 13.1 ± .9). Intraclass correlation (ICC) was used to examine the test-retest reliability of the OPAQ. The convergent validity of the OPAQ was evaluated using Caltrac accelerometers worn consecutively for 4 days (N = 51, mean age = 12.6 ± .5). Spearman's rank-order correlation was used to examine the convergent validity of the questionnaire. ICCs ranged from .76 to .91 and reliability was higher for males (r = .89) than females (r = .78). Correlations between self-reported physical activity and Caltrac accelerometer counts were related to vigorous physical activity (r = .33, p = .01) and moderate to vigorous activity (r = .32, p = .02). The OPAQ has excellent test-retest reliability and acceptable validity in comparison to other measures of youth physical activity.