The main idea of this study is to describe how and in what ways the Zagreb high school students use the Internet, do they show simptoms of excessive Internet use and whether they differ by gender, participation in leisure activities, grade they attending and their average score. For this purpose we used Internet Use Disorder Scale, the Leisure Activities Scale and some issues related to Internet usage habits. The research was conducted with 307 second and fourth grade high school students. First, metric characteristics of Internet Use Disorder Scale were verified then we examined the habits of Internet use. In the third part of the study participants were divided into two groups depending on the results on the Internet Use Disorder Scale. Group 1 was consisted of those participants who show no symptoms of excessive Internet usage and Group 2 of those participants who show mild sym symptoms of excessive Internet usage. Two groups were compared by their interent habits, leisure activities, gender, grade they attending and their average score. Results suggest one-factor structure of Internet Use Disorder Scale with acceptable internal consistency. Most participants experienced some of the symptoms of excessive Internet usage (54%). The participants spend more time on the Internet over the weekends then on the work days where a large percentage of that time is spent on online socializing and communication. They are most often connected after school, before learning and doing the homework through home computer or a smart phone. Participants in Group 2 significantly spend more time on the internet on work days rather then on weekends. More common are active online throughout the day, often playing games, browsing the Internet, commenting on statuses on social networks and downloading content from the interent. According to the results there are no significant differences between two groups regarding gender, participation in leisure activities, gender, grade they attending and their average score