Background and Aims: Social anxiety disorder (SAD) is highly prevalent among adolescents. This study aimed to assess the prevalence and associated factors of social anxiety disorder and its effect on the academic performance among medical students at Taibah University in Saudi Arabia. Methods: This cross-sectional study was conducted among 504 medical students. The social anxiety disorder (SAD) was measured by the validated Social Phobia Inventory (SPIN) questionnaire. Results: Most participants were females (56.2%) and aged ≥22 years (55.0%). Severe to very severe SAD was reported by 13.5%. Higher SAD was found among younger students ( P = 0.045), singles ( P = 0.021), those who were in their first and second academic year ( P = 0.005) and those with lower income ( P = 0.041). SAD was correlated negatively with the academic performance ( P = 0.002). Conclusion: SAD was relatively high among medical students and was correlated negatively with the academic performance. Rigorous efforts are needed for early detection and management of SAD.