We examined prevalence, treatment patterns, trends, and correlates of mental health and substance use treatments among adults with co-occurring disorders. Our data were from the 325,800 adults who participated in the National Survey on Drug Use and Health in the period 2008-14. Approximately 3.3 percent of the US adult population, or 7.7 million adults, had co-occurring disorders during the twelve months before the survey interview. Among them, 52.5 percent received neither mental health care nor substance use treatment in the prior year. The 9.1 percent who received both types of care tended to have more serious psychiatric problems and physical comorbidities and to be involved with the criminal justice system. Rates of receiving care only for mental health, receiving treatment only for substance use, and receiving both types of care among adults with co-occurring disorders remained unchanged during the study period. Low perceived need and barriers to care access for both disorders likely contribute to low treatment rates of co-occurring disorders. Future studies are needed to improve treatment rates among this population.