The purpose of this study was to assess the test-retest reliability and validity of a new Youth Physical Activity Self-Report measure. Heart rate and direct observation were employed as criterion measures with a sample of 79 children (aged 7-9 years). Spearman's rho correlation between self reported activity intensity and heart rate was 0.87 for weekday and 0.795 for weekend; the correlation between self-reported activity duration and duration as measured by heart rate were 0.837 and 0.684 for weekday and weekend, respectively. These correlations fell when recalled inactivity was excluded from analysis. A correlation of rho = 0.557 was found between self-reported activity intensity and direct observation. Results establish support for the self-report measure as an effective tool for measuring the previous day physical activity of younger children. (Contains 4 tables.)