Objective: The purpose of this review was to systematically evaluate the available heterogeneous research examining determinants of mental health service use among young adults.Methods: Nine electronic databases were searched to identify quantitative studies examining sociodemographic and psychological variables predictive of or associated with mental health service use. Included studies were examined against the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. Effect size estimates in the form of odds ratios were calculated and classified according to predisposing, enabling, and need factors, consistent with Andersen's behavioral model of health care.Results: Eighteen studies met all of the inclusion criteria (N=96,297 participants). Studies generally followed the STROBE recommendations for external validity, although limitations in internal validity were noted. Prior service contact and being homosexual or bisexual, female, or Caucasian were predisposing factors significantly associated with mental health service use. Social support was the single enabling factor identified, although this finding was based on limited data. In relation to need, young adults who reported higher perceived need for professional help or more mental health difficulties were more likely to have utilized services.Conclusions: This review identified subgroups of young adults who are less likely to access mental health support. Future research should focus on developing psychoeducational interventions targeted at young men and racial-ethnic minority groups, in addition to informing young adults of the success of mental health counseling in the absence of a diagnosis.