Little is known about the demographic and clinical characteristics of people with intellectual disabilities and substance abuse problems. Drawing on health care billing claims for people with Medicaid coverage aged 12-99 years, the characteristics of people with intellectual disability and a history of substance abuse (N = 9,484) were explored and compared with people with intellectual disability but without substance abuse. Age- and/or gender-adjusted odds ratios were derived from logistic regression analyses to consider differences in demographic and clinical diagnoses. People with intellectual disability and substance abuse constituted 2.6% of all people with intellectual disability, most of whom had a diagnosis of mild or moderate intellectual disability. People with intellectual disability and substance abuse problems were, on average, 2 years older than the comparison group and less likely to be White. The sample was more likely than the comparison group to have serious mental illness or depression and substance abuse-related disorders were not prevalent. These data provide a comparison point for existing studies of mental health diagnoses as well as new information about substance abuse disorders. Implications relate to the identification of substance abuse among people with intellectual disabilities as well as the establishment of demographic and clinical correlates.