There are approximately 6 million individuals with a diagnosis of mental retardation in the United States. Because of deinstitutionalization of patients with mental retardation, coupled with an increase in their life expectancy, emergency physicians are increasingly encountering and managing patients with mental retardation in the emergency department. Many emergency physicians are uncomfortable when interacting with individuals with mental retardation, which often carries over to the assessment and management of these patients in the ED. The purpose of this review is to aid the emergency physician in understanding the patient with mental retardation, their comorbid conditions, and the approach to evaluating and managing these patients in the ED.