Objective: Internet use may have many drawbacks. Among the main threats caused by internet use is time wasting and lack of self-control over internet use which amounts to the level of addiction with several deleterious consequences. Aim of the study is to identify the prevalence of Internet addiction (IA) and associated factors among medical students in Sohag University. Study design: a cross sectional study was conducted Methods: the cross-sectional survey was conducted in October and November 2016 on a random sample of 587 students selected from three medical faculties in Sohag University. The questionnaire used in this study was consisted of two sections The first section was concerned with securing socio-demographic data, data about student's relations and Internet use characteristics, the second one aimed at evaluating the level of Internet addiction using Young's 20- items scale (YIAT 20) for Internet addiction. Results: Findings showed that the prevalence of IA among the studied population was 47.7%. Male gender, access Internet on mobile phone, easy Internet access at home, using Internet for browsing social media and E mail and bad relation with the family were the most important predictors of IA. Conclusion: The high prevalence of IA among medical students in Sohag University (47.7%) is a matter of concern. Identification of factors significantly associated with IA can help in the planning of comprehensive programs to raise public awareness about hazards and determinants of IA targeting the high risk groups.