•Few contemporary cross-national studies have examined young adult homelessness.•We found a similar profile of co-occurring problems in Victoria and Washington State.•Unemployment, antisocial behavior and victimization co-occurred with homelessness.•Young adults with higher weekly income were less likely to report homelessness.•Understanding longitudinal and modifiable predictors of homelessness are warranted. Homelessness is associated with various co-occurring health and social problems yet; few contemporary international studies have examined these problems in young adulthood. This descriptive study presents cross-state comparison of the prevalence of young adult homelessness in Washington State, USA and Victoria, Australia using state representative samples from the International Youth Development Study (IYDS; n = 1945, 53% female). Associations between young adult homelessness and a range of co-occurring problems were examined using a modified version of the Communities That Care youth survey. Results showed significantly higher rates of past year homelessness were reported by young adults in Washington State (5.24% vs. 3.25% in Victoria). Cross-state differences were evident in levels of friends’ drug use, antisocial behavior, weekly income and support from peers. Unemployment (Adjusted Odds Ratio AOR = 2.67), antisocial behavior (AOR = 3.54) and victimization (AOR = 3.37) were more likely among young adults reporting homelessness in both states. Young adults with higher weekly income were less likely to report homelessness (AOR = 0.69) in both states. No significant association between mental health problem symptoms, substance use, family conflict or interaction with antisocial peers and homelessness were found in either state. Rates of violent behavior were more strongly related to young adult homelessness in Washington State than Victoria. The current findings suggest that programs that enable young adults to pursue income and employment, reduce antisocial behavior and include services for those who have been victimized, may help to mitigate harm among young adults experiencing homelessness.