Convergent validity of accelerometer and electronic diary physical activity data was assessed in children with asthma. Sixty-two participants, ages 9-18 years, wore an accelerometer and reported their physical activity level in quarter-hour segments every 2 hr using the Ambulatory Diary Assessment (ADA). Moderate validity was found between physical activity data from accelerometers and ADA (average individual participant Spearman r = 0.48, SD = 0.13). Within-participant accelerometer estimates for ADA sleep, rest, and light activity were different from each other and from higher activity (mixed model p less than 0.0001), but moderate did not differ from strenuous activity (p = 0.70). Moderate validity between accelerometer and electronic diary data supports the use of ADA with short-term recall to capture gross changes in daily activity. (Contains 3 tables and 3 figures.)