OBJECTIVES: Mental health disorders are highly prevalent among university students. Universities could be an optimal setting to provide evidence-based care through the Internet. As part of the World Mental Health International College Student initiative, this systematic review and meta-analysis synthesizes data on the efficacy of Internet-based interventions for university students' mental health. METHOD: A systematic literature search of bibliographical databases (CENTRAL, MEDLINE, and PsycINFO) for randomized trials examining psychological interventions for the mental health (depression, anxiety, stress, sleep problems, and eating disorder symptoms), well-being, and functioning of university students was performed through April 30, 2018. RESULTS: Forty-eight studies were included. Twenty-three studies (48%) were rated to have low risk of bias. Small intervention effects were found on depression (g = 0.18, 95% confidence interval [CI; 0.08, 0.27]), anxiety (g = 0.27, 95% CI [0.13, 0.40]), and stress (g = 0.20, 95% CI [0.02, 0.38]). Moderate effects were found on eating disorder symptoms (g = 0.52, 95% CI [0.22-0.83]) and role functioning (g = 0.41, 95% CI [0.26, 0.56]). Effects on well-being were non-significant (g = 0.15, 95% CI [-0.20, 0.50]). Heterogeneity was moderate to substantial in many analyses. After adjusting for publication bias, effects on anxiety were not significant anymore. DISCUSSION: Internet interventions for university students' mental health can have significant small-to-moderate effects on a range of conditions. However, more research is needed to determine student subsets for which Internet-based interventions are most effective and to explore ways to increase treatment effectiveness.