OBJECTIVE: To examine prevalences of substance use disorders (SUD) and comprehensive patterns of comorbidities among psychiatric patients ages 18-64 years (N = 40,099) in an electronic health records (EHR) database. METHOD: DSM-IV diagnoses among psychiatric patients in a large university system were systematically captured: SUD, anxiety (AD), mood (MD), personality (PD), adjustment, childhood-onset, cognitive/dementia, dissociative, eating, factitious, impulse-control, psychotic (schizophrenic), sexual/gender identity, sleep, and somatoform diagnoses. Comorbidities and treatment types among patients with a SUD were examined. RESULTS: Among all patients, 24.9% (n = 9984) had a SUD, with blacks (35.2%) and Hispanics (32.9%) showing the highest prevalence. Among patients with a SUD, MD was prevalent across all age groups (50.2-56.6%). Patients aged 18-24 years had elevated odds of comorbid PD, adjustment, childhood-onset, impulse-control, psychotic, and eating diagnoses. Females had more PD, AD, MD, eating, and somatoform diagnoses, while males had more childhood-onset, impulse-control, and psychotic diagnoses. Blacks had greater odds than whites of psychotic and cognitive/dementia diagnoses, while whites exhibited elevated odds of PA, AD, MD, childhood-onset, eating, somatoform, and sleep diagnoses. Women, blacks, and Native American/multiple-race adults had elevated odds of using inpatient treatment; men, blacks, and Hispanics had increased odds of using psychiatric emergency care. Comorbid MD, PD, adjustment, somatoform, psychotic, or cognitive/dementia diagnoses increased inpatient treatment. CONCLUSION: Patients with a SUD, especially minority members, use more inpatient or psychiatric emergency care than those without. Findings provide evidence for research on understudied diagnoses and underserved populations in the real-world clinical settings.