Background and Objectives: Internet addiction is one of the challenges of students that may affect their academic performance and cause stress. One of the metabolic changes related to stress is the salivary cortisol level. This study aims to evaluate the relationship of internet addiction with perceived stress, salivary cortisol level, and academic failure in dental students. Methods: In this descriptive-analytical study with a cross-sectional design, 123 dental students from Qom University of Medical Sciences participated. They were selected by a census sampling method. A demographic form, the internet addiction test, and the perceived stress scale were completed by them. Their academic failure was assessed and their salivary cortisol level was measured by the ELISA method. Data were analyzed using ANOVA, t-test, Pearson correlation test, and regression analysis. Results: Internet addiction had a positive and significant relationship with perceived stress (r=0.21, P=0.003) and its two domains of negative perception (r=0.301, P=0.005) and positive perception (r=0.279, P=0.009). However, it had no significant relationship with salivary cortisol level (P=0.123) or academic failure (P=0.614). Conclusion: It seems that decreasing internet addiction can reduce the perceived stress of dental students.