Background: Modern day life is turning towards more and more devices and internet fever is just spreading like wild  re. For young people the life is just meaningless without internet, for some it’s just like oxygen without which it’s impossible for them to survive. Excessive use, which may be accompanied by impaired sense of the passage of time and/or neglecting basic drives and withdrawal may be manifested as anger, tension or depression. Objective: To study the proportion of Internet addiction and its determinants among medical undergraduate students. Materials and Methods: A cross-sectional study was conducted among 215 medical students of Subbaiah Institute of Medical sciences, Shimoga for a period of 2 months (July–September 2017) with the help of semi-structured questionnaire consisting of questions related to demographic information, information related to internet use, and Young’s internet addiction test. Results: We found that the proportion of internet addiction among medical students was 63.7% (mild 61%, moderate 38%, severe 0.7%) and signi cantly associated factors with internet addiction being age, year of study and number of years since using internet. More than 50% students use internet for whatsApp (78%), you Tube (74%), Facebook (68%), communicating friends and family (66%), Instant messaging (54%) and scienti c search (51.6%). Conclusion: Medical students are vulnerable for internet addiction and efforts should be taken to increase awareness and prevent the problem of internet addiction in them Keywords: Internet; Addiction; Medical students.