The purpose of this research was to investigate the effects of prosocial videogames, played both singly and cooperatively, and aggressive videogames, played both singly and competitively, on children's prosocial behavior. Eighty boys and 80 girls, half third and fourth graders, and half seventh and eighth graders, were randomly assigned to one of five conditions. In a control condition, children answered questions about videogame experience and enjoyment. In two of the treatment conditions, children played a videogame with prosocial content (a human-like fantasy character rescuing another from danger); half of the children played this game singly, while the other half played cooperatively. In the other two conditions, children played an aggressive videogame (stylized boxing), with half of the children playing singly and the other half competing. Following exposure to one of these conditions, each child's game score, game enjoyment rating, level of donating, and level of helping were measured. The results of a three-way analysis of variance (sex x grade x treatment) on donating yielded significant effects for age, F(1, 140) = 34.12, p = Although prosocial videogame play did not increase prosocial responding, aggressive videogame play clearly suppressed this behavior. The failure of the prosocial condition to accelerate donating and helping might be due to the relatively brief exposure used in this study (10 minutes) and/or to the particular prosocial videogame utilized. The failure of the cooperative and competitive game modes to affect prosocial behavior may have been due to the age of the children or to the possibly aversive effects of the type of cooperation required.