We describe a child with dysmorphic features, as well as developmental and growth delay, who developed neuroblastoma at 5 mo of age. Cytogenetic analysis of blood lymphocytes revealed an interstitial deletion of 1p36.1-->1p36.2, which was apparent only with high-resolution banding. Molecular analysis with a collection of polymorphic DNA probes for 1p confirmed an interstitial deletion involving subbands of 1p36. Deletions of this region are a common finding in neuroblastoma cells from patients with advanced stages of disease. Therefore, these results (a) suggest that constitutional deletion of this region predisposed the patient to the development of neuroblastoma and (b) support the localization of a neuroblastoma tumor-suppressor locus to 1p36.