Psychiatric comorbidity likely contributes to driving under the influence (DUI) of alcohol among repeat offenders. This study presents one of the first descriptions of the prevalence and comorbidity of psychiatric disorders among repeat DUI offenders in treatment. Participants included all consenting eligible admissions (N = 729) to a 2-week inpatient treatment facility for court-sentenced repeat DUI offenders (i.e., offenders electing treatment in place of prison time) from April 17, 2005, to April 23, 2006. Participants completed the Composite International Diagnostic Interview, which assessed the following disorders using criteria from the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994): alcohol use and drug use, bipolar, generalized anxiety, posttraumatic stress, intermittent explosive, conduct, attention deficit, nicotine dependence, pathological gambling, and major depressive. Repeat DUI offenders evidenced higher lifetime and 12-month prevalence of alcohol use and drug use disorders, conduct disorder, posttraumatic stress disorder, generalized anxiety disorder, and bipolar disorder compared with the general population. Almost half qualified for lifetime diagnoses of both addiction (i.e., alcohol, drug, nicotine, and/or gambling) and a psychiatric disorder. Lifetime and past-year comorbidity rates were higher among participants than in the general population. These results suggest that clinicians should consider multimorbidity within DUI treatment protocols.