To define diagnostic criteria for Cockayne Syndrome (CS) and to identify in detail the complications of the condition, a comprehensive review of 140 cases of CS was performed. Criteria required for the diagnosis include poor growth and neurologic abnormality; other very common manifestations include sensorineural hearing loss, cataracts, pigmentary retinopathy, cutaneous photosensitivity, and dental caries. The mean age of death in reported cases is 12 3/12 years, though a few affected individuals have lived into their late teens and twenties. Prenatal growth failure, congenital structural eye anomalies, severe neurologic dysfunction from birth, and the presence of cataracts within the first 3 years of life are predictors of severe disease and early death. In contrast with other disorders of chromosome or DNA repair, cancer has never been reported in a classical CS patient, and there appears to be no predisposition to infectious complications. The wide spectrum of symptoms and severity of the disease suggest that biochemical and genetic heterogeneity exist. CS is an uncommon but devastating genetic condition which will be better understood as the biochemical interrelationships between DNA replication and repair, and between growth, homeostasis, and oncogenesis are unraveled.