Objectives: The relationship between social network risk (alcohol-using close friends), perceived peer closeness, substance use, and psychiatric symptoms was examined to identify risk and protective features of college students' social context. Participants: Six hundred and seventy undergraduate students enrolled in a large southeastern university. Methods: An online survey was administered to consenting students. Results: Students with risky networks were at a 10-fold increase of hazardous drinking, 6-fold increase for weekly marijuana use, and 3-fold increase for weekly tobacco use. College students' who feel very close to their peers were protected against psychiatric symptoms yet were at increased risk for marijuana use. Perceived closeness of peers was highly protective against psychiatric symptoms, adding a natural preventive effect for a population at great risk for mental illness. Conclusions: Results support targeting college students through network-oriented preventive interventions to address substance use as well as mental health.