Deletion of chromosome 1p and MYCN amplification have been reported as frequent abnormalities in human neuroblastoma. We studied loss of heterozygosity (LOH) in 50 (48 informative) Italian neuroblastoma patients by restriction fragment length polymorphisms (RFLPs) analysis using anonymous and hypervariable region (HVR) sequences. Twelve cases (25%) showed LOH at one or more loci. Locus D1S94 was the most frequently involved in LOH events (8/12) of deleted cases (66.6%). MYCN amplification was observed in 20% of patients which showed a significantly lower event-free survival probability (EFSp) (P = 0.004). We also studied the allelic distribution in the constitutional DNA of neuroblastoma patients (n = 44) and a matched group of healthy Italian subjects (n = 79) for loci D1S112 and D1S94. A significantly (P = 0.01) different allele frequency was detected for the two groups at locus D1S94, but not at D1S112. Moreover, the neuroblastoma population did not confirm the Hardy-Weinberg expectations at the former locus. This observation suggests the existence of an allelotype associated with neuroblastoma susceptibility.