The purpose of the current study was to identify characteristics contributing to or hindering utilization of mental health services in the past 12 months among working age adults with mental illness using Andersen's Behavioral Model of Health Services Utilization. Originally developed in 1968, Andersen's model hypothesizes that three sets of factors, (predisposing, enabling, and need) differentially impact health services utilization. Historically mental health services have been underutilized in the U.S. and have unique mechanisms for care and reimbursement that are less prevalent for general health services. The current study utilized data from the National Survey on Drug Use and Health, a population based-survey capturing patterns of drug use, mental health, and health services use in U.S. households of individuals 12 and older. The current study focused on mental health data for adults aged 18-64 who met criteria for mild, moderate, or serious mental illness. All data were publically available through the Substance Abuse and Mental Health Services Administration and SSPS 22 was used to analyze data. Statistical analyses included descriptive frequencies, bivariate logistic regression, and multivariate logistic regression with odds ratios reported. The final sample included 7,335 respondents. More than half of participants did not receive any mental health treatment. Among predisposing factors, being female and age 35 or older were associated with a greater likelihood of service utilization while being a race other that Non-Hispanic white was associated with a decreased use of services. Among enabling factors, individuals not currently working and having public insurance increased mental health service utilization. Individuals who had up to a high school diploma or GED, lacked insurance coverage, and made less than $10,000 annually were less likely to use mental health services. Among need factors, having moderate or serious mental illness and reporting unmet need was associated with an increased use of mental health services. Cost was the most reported reason for unmet need followed by thinking they could handle the problem without treatment for both users and non-users of mental health services. In order to increase the use of mental health services, future policy and treatment interventions should focus on enabling factors.