Ag-NOR number and ploidy have potential use in predicting prognosis in malignancy. The issue of independence has not been conclusively studied. In contrast to other malignancies in neuroblastoma poor outcome is linked to diploidy, allowing independent analysis of the reaction of Ag-NOR status to outcome.A consecutive unselected series of 20 pediatric neuroblastoma patients was used to study the relation between ploidy and mean Ag-NOR number per nucleus. Ploidy was established by flow cytometric analysis of nuclear suspensions prepared from Formalin fixed and paraffin embedded tissue. The mean number of Ag-NORs per nucleus was determined using 3-microns paraffin sections, silver staining methods and quantification procedures detailed in the literature.The seven diploid lesions were found to have a mean Ag-NOR number per nucleus of 4.38 (range 0.86-7.5). The 13 aneuploid lesions were found to have a mean Ag-NOR number per nucleus of 2.31 (range 1.17-4.44). Probability of difference (Wilcoxon's two-tailed rank sum test) was greater than 99%. Nonsurvivors (6 of 10 diploid) had mean Ag-NOR number per nucleus of 4.34 (range 2.24-7.5). Survivors (9 of 10 aneuploid) had mean Ag-NOR number per nucleus of 1.73 (range 0.86-2.56). Probability of difference (Wilcoxon's two-tailed rank sum test) was greater than 99%. In aneuploid lesions (n = 13) a negative correlation exists between DNA index and mean number of Ag-NORs per nucleus (correlation coefficient 0.84, slope -0.74, probability of noncorrelation less than 0.010).The present observations offer the first independent support to the theory that Ag-NOR number is an independent variable to DNA ploidy based on the unique feature of neuroblastoma that diploid lesions have an established poorer prognosis than aneuploid lesion. The observations, although the number of cases is too limited for independent analysis, confirm previously published, strong negative relations between mean Ag-NOR number per cell and survival in childhood neuroblastoma. This relation is similar to findings in other solid tumor lesions.