Background: This systematic review aimed to identify the factors related to psychosocial outcomes for adults with high-functioning autism spectrum disorder (HFASD). A further aim was to appraise the research methodology and provide recommendations for future research. Method: Systematic review methodology was used to comprehensively search for peer-reviewed articles, assess methodological rigor, and summarise the results. Twenty-seven studies published between 1989 and December 2015 met inclusion criteria and included 1,398 individuals (M age = 28.54 years) with HFASD (IQ = 70). Results: Factors most consistently found to be related to poor psychological, social, and adaptive outcomes included greater symptom severity, lower childhood IQ, impaired nonverbal learning, cognitive shifting deficits, negative thinking styles, and perceptions of low social support. Conclusions: Overall, key risk factors for poor psychosocial outcomes of adults with HFASD were identified. However, further prospective longitudinal research with large samples is needed to examine the complex and potentially bidirectional relationships among these factors.