Internet addiction is of growing concern and college students are particularly vulnerable. This study examines the mediating effect of dysfunctional attitude on the association between psychopathology (depression and social anxiety) and Internet addiction among Korean college students. A sample of 159 college students from one university was obtained via an online survey. Participants completed a depression scale, social avoidance and distress scale, dysfunctional attitude scale, and Internet addiction test. Overall, 25.8% of students were classified as problematic Internet users. Use of the Internet for gaming and general Internet use time were significantly associated with Internet addiction, and specific uses of the Internet differed by gender. In multiple regression and mediation analyses with bootstrapping, dysfunctional attitude completely mediated the association between depression and Internet addiction, and partially mediated the association between social anxiety and Internet addiction. The assessment for those at risk of Internet addiction should include evaluation of depression, social anxiety, and dysfunctional attitude. The mediation role of dysfunctional attitude indicated the need for nurses to attend not only to psychopathology but also to cognition regarding problematic Internet use, particularly for college students.