Prior research demonstrates that persons with co-occurring substance use and mental problems tend to have higher needs and receive less-than-optimal care, yet it is not known what factors predict such mismatch in service need and use. The aim of the article is to explore client characteristics associated with a mismatched level of care for persons with and without co-occurring disorders within a provincial community mental health system. For this, standardized assessments were completed by trained clinical staff for 5051 cases, representing 41,051 individuals enrolled across 407 community mental health programs. Assessments consisted of the Colorado Client Assessment Record and a Support and Service Profile from which co-occurring disorder status and global indices of current and recommended levels of care were derived. Thirteen client-level variables were entered as main effects and as interaction terms (with co-occurring disorder) in a logistic regression to predict whether clients were underserved at two or more levels below recommended levels. Having a co-occurring disorder significantly increased the odds of under-service nearly tenfold (OR ¼ 9.94). Six other variables predicted under-service: having a personality disorder, not working, not completing high school, having criminal justice system involvement, high overall problem severity and being male (OR range ¼ 2.95-1.35). Within the cooccurring disorder group, only two variables, having schizophrenia and not being on medication, emerged as significant independent predictors of underservice. While having a co-occurring disorder is associated with receiving less overall care in general, the findings illustrate that schizophrenia and medication use are important contributing factors.