A role of beta-catenin (CTNNB1) in the molecular pathogenesis of adrenocortical carcinoma (ACC) has been suspected in adult ACC and pediatric pigmented nodular adrenocortical disease, but it has never been reported in pediatric ACC. We present the case of a 4-month-old Thai infant who had Cushing's syndrome secondary to bilateral adrenal tumors with hepatic metastasis. The child was successfully treated with a bilateral adrenalectomy and wedge resection of the liver nodule. Histopathology revealed bilateral adrenocortical tumors with different histologic grades; the right tumor had a higher score, according to modified Weiss criteria. On molecular study, a deletion mutation of beta-catenin involving codons 44 to 45 was detected in the right adrenal tumor. The same mutation was found in peripheral blood before treatment; this mutation disappeared after tumor removal. The left tumor harbored wild-type beta-catenin. Immunohistochemistry showed nuclear accumulation of beta-catenin on the right adrenal tumor and the metastatic nodule. In summary, we present evidence that supports the role of the Wnt-signaling pathway in the carcinogenesis of pediatric adrenocortical carcinoma.