Prognostic markers in pediatric adrenal cortical tumors are difficult to define. We determined the ploidy, immunostaining of p53-protein and number of nucleolar organizer regions (AgNORs) in 16 such tumors and related them to clinical outcome, tumor weight (TW) and histologic Weiss' criteria. Eleven females and 5 males aged 0.4 to 15.6 years were followed for 8.7 years; 10 presented Cushing's and 6 virilization syndrome. Diploid (n = 4, x TW = 269 g, range: 17-800 g) and near-diploid tumors (n = 3, x TW = 55 g, range: 20-85 g) had good outcome, Weiss' criteria were 0-7, and p53 reactivity was negative in all. Among the aneuploid tumors (n = 9, x TW = 298 g, range: 7-1000 g), 6 had good outcome, 2 presented metastasis and 1 was lost to follow-up; Weiss' criteria were 2-8 and p53 reactivity was positive in 3 tumors (2 of them of malignant evolution). AgNORs number was not different in cases of good or poor outcome (3.65 +/- 1.9 vs 2.83 +/- 1.1). Our findings indicate that diploid and near-diploid cases had always a good outcome regardless of tumor weight. In aneuploid cases, tumor weights < 100 g had good outcome, while those > 750 g had poor prognosis. Malignant tumors were aneuploid and had reactivity to p53-protein. Good outcome in aneuploid tumors < 100 g is probably due to early treatment. The expression of p53-protein appears as a promising marker of poor prognosis. Weiss' criteria and AgNORs were not useful in the present series.