Adrenocortical carcinoma (ACC), a very rare tumor in children in the United States, is apparently more common among Brazilian children. We reviewed the medical records of 40 children whose disease was diagnosed between 1966 and 1987. There were 12 boys and 28 girls; their median age was 3.9 years (range, 1 day to 15.7 years). Virilization was the most common clinical sign (37 of 40); other signs included abdominal mass, deepened voice, plethora, hypertension, seizures (seven patients) and, rarely, weight loss (two patients). The median time between first signs or symptoms and diagnosis was 1.4 years (range, 3 days to 5 years). Four of 33 tumors were classified as benign according to the Weiss, van Slooten, or Hough systems (tumor tissue was unavailable for seven patients). Tumors were completely resected in 26 of 38 patients; of those, 17 are in continuous complete remission, five relapsed, and four have been lost to follow-up. One patient, who had local recurrence, has been in a third complete remission for 18+ months after tumor resection and chemotherapy (cisplatin and etoposide). Of the remaining 14 patients, 11 died of progressive disease, the diagnosis was confirmed at autopsy in two, and one has been lost to follow-up. Univariate analysis disclosed that age greater than or equal to 3.5 years at diagnosis, interval of greater than or equal to 6 months between first symptoms and diagnosis, tumor weight greater than 100 g, tumor size greater than 200 cm3, and high levels of urinary 17-ketosteroids (17-KS) and 17-hydroxycorticosteroids (17-OH) were associated with an unfavorable outcome. Multivariate analysis disclosed that only a tumor size greater than 200 cm3 independently identifies those patients with an unfavorable prognosis. Among the variables known before surgery, age, and the interval between first symptoms and diagnosis were important predictors of outcome. Our data suggest that some children with ACC and certain clinical characteristics are at high risk of primary treatment failure and, therefore, are good candidates for investigational adjuvant therapy.