Patients with Niemann-Pick type D have been traced to a single Acadian ancestor in Nova Scotia. The objective of this study was to describe the clinical course. A cohort of children with Niemann-Pick type D was identified by chart review. Some children were seen and a telephone interview with the remaining parents was conducted. Twenty children with Niemann-Pick type D were identified. The female to male ratio was 2:1. Five children had severe neonatal jaundice. Early milestones were normal in the majority. Neurologic symptoms generally developed between 5 and 10 years of age with a mean age of 7.2 years at diagnosis. Seizures developed in all between 4.5 and 16 years of age (mean, 10.5 yr), and were followed by significant physical and mental deterioration. The age at death ranged between 11 and 22.5 years (mean, 14.8 yr). In 61%, bronchopneumonia was the cause of death. There is significant variability in the presentation and clinical course of Niemann-Pick type D.