Nonadherence to medications in cancer treatment protocols may be a particular concern among adolescents and young adults (AYAs) with cancer and predictive of poor health outcomes, but data supporting this claim remain limited. The purpose of this article was to systematically review the rates, outcomes, and predictors of oral medication nonadherence among AYAs with cancer. PubMed (i.e., MEDLINE), CINAHL, and PsycINFO databases were searched in 2018 using terms related to medication adherence and cancer. A total of 37,884 records representing 34,006 unique articles were identified and reviewed. Thirteen articles representing 12 studies met inclusion criteria and examined medication adherence among AYAs with cancer. Results of these studies suggest that 21%-60% of AYAs are nonadherent to oral medications, likely placing them at increased risk for poor health outcomes (i.e., relapse, infection/fever, and death). Psychosocial factors (i.e., knowledge, beliefs about capabilities, beliefs about consequences, environmental context and resources, and emotion) were related to nonadherence and warrant future study. Of note, demographic, disease, and family composition variables did not predict nonadherence. Clinical implications as well as limitations and resulting future directions are discussed.