In recent years, a substantial amount of research has been devoted to the use and excessive use of the Internet (Young, 2004). In this paper, we present the results of a sample survey which was carried out among a random sample of 1876 Greek University students examining, for the first time, the consequences of heavy and non heavy Internet use. Multivariate Analysis of Variance (MANOVA), F- tests and t-tests were applied and the results showed that heavy Internet users compared to non heavy Internet users had more problematic interpersonal relations with parents, teachers, friends, were more depressed, lonely and with low self esteem, had a more disappointing academic performance and they were dependent on a greater percentage on alcoholism, smoking, drinking coffees and taking substances.