The issue of Internet addiction has so far not been in the centre of attention of researchers studying the impact of online technologies on children and possible risks they are encountering in the cyberspace. In search for the risk factors, research has mostly focused on the characteristics of children's online activities and on the content of computer-mediated communication rather than on the potential negative effects of the amount of time spent by children online on their psychological development and social life (needles to say, this problem is almost completely neglected by descriptive studies comparing the access to Internet across countries and measuring digital gaps and divides between them). Drawing on psychological conceptualizations of 'Internet addiction' and on existing body of research on this topic, our aim in this paper is to empirically examine patterns of Internet addiction among teenage Internet users in the Czech Republic. The data for the analysis are used from the 'World Internet Project: Czech Republic' survey, which was conducted in September 2007 on a representative sample of 1586 respondents. From these, there were 224 respondents aged between 12 and 19 who claimed to be Internet users. As a main research instrument, a battery of 14 questions measuring potential Internet addiction (based on already existing studies and concepts) was included in the questionnaire. For the purpose of the analysis, a composite measure was created out of the individual responses: an index of Internet addiction. The preliminary findings show that there is a negative correlation between age and the addiction score, indicating that the adolescent respondents (particularly teenagers aged 16 to 19) have a higher potential for addiction than the adult ones. Even though there is no significant difference between the age groups 12 to 15 and 16 to 19 in the addiction level, the older group exhibits higher awareness of the possible negative effects of their amount of Internet usage (according to their scores on the scale of self-perceived addiction), which means that the youngest children are potentially more vulnerable in regards to Internet addiction. Examining other factors which influence Internet addiction, we determined that there is no difference in gender or region; both the girls and boys have exhibited similar scores, and the same goes for the geographical region or the size of domicile. The activities which displayed highest correlations with the addiction index were downloading videos and music, listening to online radios but also taking part in online discussion groups. This, together with the finding that the addiction score grows with the number of online friends, points to the fact that researching the problem of Internet addiction always has to be properly contextualized and should be connected with the research on online networks and communities.