Nuclear DNA content and N-myc amplification have been found to have prognostic significance in neuroblastoma. To investigate the interrelationships between these two parameters, tumor samples from 18 patients with neuroblastoma were analyzed for both total DNA and N-myc gene content. Quantitative DNA analysis was performed by image analysis. Quantitative Southern blot hybridization was used to determine N-myc gene copy number and to distinguish between low level gene amplification or excess gene copies secondary to aneuploidy. Six of the 18 patients have died. Five of the six had nonaneuploid tumors, but only two of the six exhibited major N-myc amplification. Low-level amplification was detected in one Stage II patient. The authors' results suggest that neuroblastomas with N-myc amplification are a subset of nonaneuploid tumors.