Aim To estimate the percentage and risk factors of Internet addiction (IA) at Greek Internet cafés. Methods We used a questionnaire including questions on demographics, Internet use duration, Internet applications and sites visited, degree of Internet use influence on daily schedule and social relations, psychosocial characteristics of users and Young's IA Test (48 items overall). Our randomly selected sample included Internet café users in Athens and other big Greek cities. The sample size was 686 people (74%/26% M/F) and 12%, 70% and 18% were between 7–14, 15–25 and 26–45 years old respectively. Results Cronbach's alpha ranged from 0.79 to 0.90 for all 6 sections of our questionnaire. The prevalence of IA among Internet café visitors was 20.8% (16.0% men, 4.8% women). IA was significantly associated to Internet use duration per day, Internet Café visits number per week, number of hours playing at Internet cafés per visit, duration playing violent games (e.g. Counter-Strike, Quake, Assassin), duration visiting Facebook and MySpace, and degree of Internet use influence on daily schedule, social relations and psychological attitudes (p < 0.01). Binary logistic regression showed that significant predictive factors of IA were the length of time playing violent games [ORCounter-Strike = 23.6 (95% CI 1.2 − 40.1); ORAssassin = 10.9 (95% CI 1.5 − 43.2)], visiting Facebook [OR = 41.9 (95% CI 19.7 − 87.5)], and deterioration of social relations (p = 0.009). Conclusion IA is frequent in Internet cafés, possibly due to an online gaming addiction affecting multiple aspects of a person's life.