Young children who played video games every day had later sleep and wake times (P < 0 .001) and were more evening-typed (P < 0.001) than those who did not every day in the both countries. The longer Czech children played video games per time, the later sleep and wake times were (P < 0.001). Czech children who played video games from 18:00 - 21:00 showed later sleep times and shorter sleep hours (P < 0.001) on weekdays than those who played at earlier times. Japanese children who played video games from 18:00 - 21:00 were more evening-typed and woke up later than those who played at earlier times (P < 0.001). Czech children who had their own video game devices had a higher frequency of anger than those who did not (P < 0.001). Ha- bitual video game playing in the evening may make children more evening-typed and it may also be speculated to make them more aggressive in both countries.