Specific constitutional chromosome rearrangements have been described in a small number of individuals with two solid childhood tumors, retinoblastoma and Wilms' tumor. On the basis of these observations, a causal relationship between these chromosome abnormalities and tumorigenesis has been postulated. Though a specific constitutional chromosome abnormality has yet to be reported in association with neuroblastoma, another childhood tumor, we now confirm the involvement of a particular chromosome segment in structural abnormalities in cells from this tumor. Deletions or rearrangements of chromosome 1p were found in preparations from four of six neuroblastomas from individuals with normal constitutional karyotypes and in three of four permanent neuroblastoma cell lines. Structural abnormalities resulting in the loss or rearrangement of material from 1p (with the most frequent break point being 1p32 and with all rearrangements involving the apparent loss or rearrangement of material distal to 1p31, always including 1p34 to 1pter), represent the single most common class of chromosome aberrations in neuroblastoma. This suggests that the distal portion of 1p contains at least one gene involved in the development of neuroblastoma.