Behavior analysis has made contributions in the development of evidence-based interventions for people with intellectual and developmental disabilities (IDD), and there is a growing evidence base for behavior-analytic interventions for older adults with dementia. As there is an increased number of adults with IDD living to old age, and an increased prevalence of comorbid dementia in people with IDD, a review of the behavior-analytic contributions with this population is warranted. We searched Web of Science and PsycInfo and manually reviewed the last 20 years of five behavioral journals. Six behavior-analytic studies with people with IDD and dementia were identified, and all but one were published outside of core behavior-analytic journals. These articles were analyzed in terms of Baer, Wolf, and Risley’s (Journal of Applied Behavior Analysis, 1, 91–97, 1968) seven dimensions of applied behavior analysis (ABA). The possible explanations and implications of these findings are discussed with consideration of the unique features of a comorbid diagnosis of IDD and dementia that may make it appropriate for increased focus in behavior-analytic research and practice.