Childhood neuroblastoma, an embryonal neoplasm of sympathetic nervous system progenitors, occurs in a familial form with an autosomal dominant mode of inheritance. Genetic susceptibility to this disorder is thought to arise via a germline mutation affecting a tumor suppressor gene, in accord with the two-hit model established for familial and sporadic retinoblastoma. Surprisingly, the familial neuroblastoma predisposition locus does not map to chromosome band 1p36, a genomic region likely to contain one or more neuroblastoma suppressor genes. We reasoned that inherited point mutations affecting one allele would be unmasked in many cases by somatically acquired deletions of the second allele that included the target gene in the tumor cells from these patients. Thus, to identify chromosomal regions that might contain suppressor genes important in hereditary neuroblastoma, we analyzed six familial tumors by comparative genomic hybridization. Recurrent losses of genetic material were detected on chromosome arms 3p (consensus region, 3p24-pter), 10p (consensus, 10p12-p13), 10q (consensus, 10q25-qter), 16q (consensus, 16q12-q22), and 20q (consensus, 20q13.3-qter), in addition to the regions commonly deleted in sporadic neuroblastomas (1p36 and 11q). These chromosomal sites may harbor novel tumor suppressor genes that could aid in our understanding of the predisposition to and pathogenesis of familial neuroblastoma and potentially sporadic tumors as well.