Thirty-six neuroblastomas were analysed for chromosome 1p alterations and their prognostic relevance. In 72% (26/36) of the patients, 1p alterations were identified in the tumours using 24 polymorphic loci ranging 1p22-1p36.3. LOH was identified in 25 children, and in 10 additional allelic imbalance was identified. In 1 child allelic imbalance was the sole alteration. Imbalance was termed as gain in intensity of one allele with or without reduction of the second allele (< 50%). The imbalance was identified in adjacent regions to the LOH. Two distinct regions of LOH were identified: 1p36.1-p36.3 and 1p31-p32. The common imbalance regions overlapped the common LOH regions. The children with LOH and imbalance had improved survival (100%) compared to the children with LOH only (26%) after 48 months of follow-up. The imbalance had an advantageous effect that is reflected by the improved outcome in children with other unfavourable clinical features.