Nonmedical use of prescription drugs is rising in the United States (Substance Abuse and Mental Health Services Administration, 2001; Substance Abuse and Mental Health Services Administration, 2011). Diversion of these substances represents a growing problem for law enforcement and public health officials (Cai, R., Crane, E., Poneleit, K., & Paulozzi, L., 2010; U.S. Department of Justice, 2009). This study documents the extent of prescription drug diversion among an understudied population -- individuals with legitimate prescriptions - and uses Social Learning Theory and Rational Choice Theory to examine risk factors relating to diversion. Participants: Participants in this study were 502 young adults who had been prescribed a medication in waves 5 through 7 of the College Life Study. The College Life Study is a prospective longitudinal study of a single cohort of young adults that were sampled from a large, public university in 2004. Methods: Diversion behavior was described in detail and differences between diverters and non-diverters were examined. Regression analyses examined the effects of theoretically driven peer and rational choice effects on the likelihood of diversion. Opportunity and perceptions were examined as potential mediators. Results: Individuals with legitimate prescriptions divert a substantial amount of medication. Reasons for refusing to divert, opportunities for diversion, and beliefs about diversion differ between diverters and non-diverters. Regression analyses revealed both peer effects and exposure to information regarding prescription drugs predict diversion. Opportunity mediated the relationship between perceptions of peer diversion and likelihood of diversion. Conclusions: Support for both social learning and rational choice approaches to diversion was found. Additional research is warranted to continue to explore risk and protective factors relating to diversion. Implications for the field are discussed.