Computer games are the most advanced form of gaming. For most people, the playing is an uncomplicated leisure activity; however, for a minority the gaming becomes excessive and is associated with negative consequences. The aim of the present study was to investigate computer game-playing behaviour in the general adult Norwegian population, and to explore mental health problems and self-reported consequences of playing. The survey includes 3,405 adults 16 to 74 years old (Norway 2007, response rate 35.3%). Overall, 65.5% of the respondents reported having ever played computer games (16-29 years, 93.9%; 30-39 years, 85.0%; 40-59 years, 56.2%; 60-74 years, 25.7%). Among 2,170 players, 89.8% reported playing less than 1 hr. as a daily average over the last month, 5.0% played 1-2 hr. daily, 3.1% played 2-4 hr. daily, and 2.2% reported playing > 4 hr. daily. The strongest risk factor for playing > 4 hr. daily was being an online player, followed by male gender, and single marital status. Reported negative consequences of computer game playing increased strongly with average daily playing time. Furthermore, prevalence of self-reported sleeping problems, depression, suicide ideations, anxiety, obsessions/ compulsions, and alcohol/substance abuse increased with increasing playing time. This study showed that adult populations should also be included in research on computer game-playing behaviour and its consequences.