Background: This study aimed to determine the prevalence of internet addiction and its associated factors among medical students at Taibah University in Madinah, KSA. Methods: This cross-sectional study was conducted among 426 medical students from Taibah University, KSA. The 20-item Internet Addiction Test (IAT) was used to measure internet addiction. Results: Most participants (40.8%) used the internet for 5–7 hours/day and mainly for social networking (88.5%) and for downloading media files. Approximately, 6% were classified as internet addicts and 42% had occasional problems. Internet addiction was correlated negatively with performance. Internet addiction was significantly higher among those who used the internet for more than 10 hours/day ( P < 0.001), those who used the internet mostly for downloading media files ( P = 0.005) and for social networking ( P = 0.005). Conclusion: Internet addiction among medical students is relatively high. Preventative measures like awareness campaigns are recommended to minimize internet addiction among university students.