In the present study, we tested the hypothesis that adolescents might underestimate time while playing a video game. To test this hypothesis, 116 adolescents (14–15 years old) had to judge prospectively or retrospectively the duration of three consecutive tasks: a 8 min and a 24 min task of playing video game (Tetris) and an 8 min task of reading on a computer screen (control task). The main hypothesis received support: for a same duration, the video game task was estimated as shorter than the reading task. Moreover, participants with a game-inclined profile showed a stronger underestimation of time while playing. Finally, the short durations were overestimated and the long duration underestimated. The main findings are accounted for by an attention-based explanation.