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ABSTRACT Background and Aim: The purpose of the current study was to investigate the relationship between internet addiction and depression, anxiety, stress and social phobia among students in Isfahan University. Material and Method: This is a cross-sectional study (descriptive-analytic). The study population was students of Isfahan University, in Iran. 71 students (36 girls and 35 boys) were randomly entered into the study. We used Young's internet addiction test (IAT), depression anxiety stress scale (DASS) and social phobia inventory (SPIN). The data were analysed by correlation and regression analysis. Results: The results indicated a significant correlation between internet addiction and each clinical variable (depression, anxiety, stress and social phobia (p<0.001). Also the results of regression analysis revealed a positive correlation between internet addiction and the set of these clinical variables (r=0.62). These clinical variables can predict 39% of addiction to the internet (p<0.001). Conclusion: The results of the current study implied that the set of these clinical variables (depression, anxiety, stress and social phobia) can predict internet addiction. Keywords: Internet addiction, Depression, Anxiety, Stress, Social phobia. Received: Jan 26, 2012 Accepted: May 13, 2012