OBJECTIVES: Patients with comorbid alcohol use disorders (AUD) and substance use disorders (SUD) may be identified in administrative claims data using a range of codes (eg ICD-9 303-305), but it is not clear this yields a homogenous group. The objective of this study was to characterize patients with AUD/SUD claims to better understand the resulting comorbidity measures. METHODS: Patients with ≥1 claim indicative of AUD/SUD between 2005-2012 were identified in the Truven Health MarketScan® Commercial and Medicare Research Databases. Continuous enrollment 6 months before and 12 months after the earliest AUD/SUD claim was required. Patients were analyzed overall, then stratified by earliest drug of abuse (alcohol, amphetamines, cannabis, cocaine, hallucinogens, sedatives, opioids) for bivariate comparison of patient characteristics, cost and utilization. RESULTS: The sample included 476,628 patients; most (73%) with an AUD diagnosis. Overall, the sample was mean age 39 and 63% male. Total post-index costs were mean $17,481 and median $7,332. Other cost measures were similarly skewed. Less than half (43%) had a second AUD/SUD claim ≥30 days post-index. The sedative cohort had the lowest proportion males (54%). Mean age was lowest in the hallucinogen (24 years) and cannabis (26 years) cohorts; each consisted of 35% patients <18. Over half the amphetamine cohort resided in the western and southwestern US. Major psychiatric comorbidity was present for 44% in the sedative cohort, compared to 15% in the alcohol cohort. Median total post-index costs were lowest for the cannabis ($6,740) and alcohol ($6,830) cohorts, and highest for the sedative cohort ($16,628). CONCLUSIONS: Patients with claims carrying diagnoses indicative of AUD/SUD are a highly heterogeneous group in terms of drug of abuse, demographic and clinical characteristics, and healthcare costs and utilization. Measures combining AUD and SUD patients may be more reflective of alcohol than other substances because AUD patients predominate.