Although existing evidence suggests an increased prevalence mental and behavioral health conditions for people with intellectual and developmental disabilities (IDD), little is known about health service utilization patterns related to these conditions. This study provides population-based data on hospital service utilization. Medicaid claims for people under 65 years of age in Massachusetts were used (years 2008-2013) to identify a cohort of people with IDD. Utilization of inpatient hospitalizations and outpatient Emergency Department (ED) was compared with the U.S. and MA general population through risk ratios. Findings suggest mental and behavioral health conditions were major contributors to increased utilization of inpatient and outpatient ED services and underscore the need for community-based service options that understand how to treat these conditions in people with IDD and address the myriad of related factors to identify, treat, and minimize the potential adverse life impact of these conditions for people with IDD.