This study tested the reliability and validity of measuring children's food intake with the digital photography method and the effects of second servings upon food intake. Food intake was measured in a school cafeteria for 5 days. Adiposity was assessed with body impedance analysis and body mass index, expressed as percentile rank. Mood and self-esteem were assessed with questionnaires. Estimates of food intake were highly reliable between two registered dietitians who independently estimated food intake. Boys ate more food than girls. A significant association between food intake and adiposity supported convergent validity. Non-significant correlations between food intake and depressed mood and self-esteem supported discriminant validity. When second servings were available, more food was selected and discarded, but mean food intake did not increase. Children who returned for second servings, however, ate more food when second servings were available, and a trend suggested that they also ate more food when second servings were not available. These findings support the reliability and validity of measuring children's food intake using digital photography and demonstrate its utility for studies of food intake and body weight.