Objective Excessive internet use has been associated with various psychiatric symptoms and psychosocial factors. This study aimed to investigate the prevalence of internet addiction (IA) and its associations with clinical (depression/social anxiety) and psychosocial (selfesteem/ perceived social support) factors in medical students. Methods In total, 408 medical students at one university in Korea were included in this study. IA symptoms were assessed with Young’s Internet Addiction Test, and scores of 50 or higher were considered to indicate IA. Participants were asked to complete the Beck Depression Inventory, Social Phobia Inventory, Rosenberg Self-Esteem Scale, and Duke-University of North Carolina Functional Social Support Questionnaire. A logistic regression model was constructed to examine the impact of clinical and psychosocial factors on IA. Results Forty-seven participants (11.5%) were identified as having IA. Self-esteem was associated with a lower risk of IA, whereas depression and social anxiety were associated with a higher risk of IA. Depression, social anxiety, low self-esteem, and low perceived social support were found to be significant correlates of IA. Young’s Internet Addiction Test score positively correlated with Beck Depression Inventory and Social Phobia Inventory scores, but negatively correlated with Rosenberg Self-Esteem Scale and Duke-University of North Carolina Functional Social Support Questionnaire scores. Furthermore, the prevalence of IA was highest in first-year medical students. Conclusion This study revealed the possible risk and protective factors of IA. Our findings indicate that strengthening self-esteem and reducing depression and social anxiety may contribute to the prevention and management of IA in medical students.