Childhood disintegrative disorder (CDD) is a clinical syndrome characterized by disintegration of mental functions and regression of acquired language and intellectual functions after a period of normal development typically of 3 to 4 years. Although recognized for many years, research on this condition is less advanced than that in autism. Epidemiological data are limited but the condition is much less common than autism. The relationship of this condition to autism remains the topic of debate. Neuropathological and other medical conditions are sometimes associated with the disorder but contrary to earlier belief this is not typical. Collaborative research would facilitate our understanding of this condition.