The aim of this paper is to investigate the relationships between Problematic Internet Use (PIU) among university students in Greece and factors such as gender, age, family condition, academic performance in the last semester of their studies, enrollment in unemployment programs, amount of Internet use per week (in general and per application), additional personal habits or dependencies (number of coffees, alcoholic drinks drunk per day, taking substances, cigarettes smoked per day), and negative psychological beliefs. Data were gathered from 2,358 university students from across Greece. The prevalence of PIU was 34.7% in our sample, and PIU was significantly associated with gender, parental family status, grade of studies during the previous semester, staying or not with parents, enrollment of the student in an unemployment program, and whether the student paid a subscription to the Internet (p < 0.0001). On average, problematic Internet users use MSN, forums, YouTube, pornographic sites, chat rooms, advertisement sites, Google, Yahoo!, their e-mail, ftp, games, and blogs more than non-problematic Internet users. PIU was also associated with other potential addictive personal habits of smoking, drinking alcohol or coffee, and taking drugs. Significant risk factors for PIU were being male, enrolment in unemployment programs, presence of negative beliefs, visiting pornographic sites, and playing online games. Thus PIU is prevalent among Greek university students and attention should be given to it by health officials.