There is burgeoning interest in the study of video games. Existing work is limited by the use of correlational designs and is thus unable to make causal inferences or remove self-selection biases from observed results. The recent development of online, socially integrated video games (massively multiplayer online role-playing games [MMORPGs]) has created a new experience for gamers. This randomized, longitudinal study examined the effects of being assigned to play different video game types on game usage, health, well-being, sleep, socializing, and academics. One hundred 18- to 20-year-old participants (73% male; 68% Caucasian) were randomly assigned to play arcade, console, solo computer, or MMORPG games for 1 month. The MMORPG group differed significantly from other groups after 1 month, reporting more hours spent playing, worse health, worse sleep quality, and greater interference in "real-life" socializing and academic work. In contrast, this group also reported greater enjoyment in playing, greater interest in continuing to play, and greater acquisition of new friendships. MMORPGs represent a different gaming experience with different consequences than other types of video games and appear to pose both unique risks and benefits from their use.