Emergency room (ER) and hospital utilization among people with intellectual and developmental disabilities (IDD) are significant contributors to rising healthcare costs. This study identifies predictors of utilization among 597 adults with IDD. Using a retrospective survey of medical charts, descriptive statistics and logistic regressions were conducted. Individual-level risk factors for ER utilization included age, number of chronic health conditions, a diagnosis of cerebral palsy or neurological disorder, mental illness, and polypharmacy. Environmental predictors included community-based supported living. Hospitalization predictors included age and number of chronic illnesses. People residing in group homes were less likely to be admitted. This study found risk factors unique to individuals with IDD that should be addressed with tailored interventions as states transition to Medicaid managed care.