Adrenal cortical tumors are rare in children. Secondary tumors associated with untreated congenital adrenal hyperplasia (CAH) have also been reported in pediatric population. It is difficult for pediatricians to differentiate these 2 lesions.We described a 4.5-year-old girl who presented with symptoms and signs of virilization. Bone age was 9.5 years. Genetic analysis of CYP21A2 and CYP11B1 revealed a heterozygous mutation of CYP11B1 at c.1157C>T (A386V). No germline p53 gene mutation including R337H was detected.The patient was first misdiagnosed as CAH and treated with hydrocortisone for 3 months. Diagnosis of an adrenal cortical tumor was confirmed by laboratory data and abdominal computed tomography. After resection of the tumor, serum steroids normalized and clinical signs receded. The child received no additional treatment and remains disease free after 12 months of close observation. Histological examination showed neoplasia cells with predominantly eosinophilic cytoplasm and few atypical mitotic figures. The proliferation-associated Ki-67 index was <1% detected by immunohistochemistry.Neoplasm is a rare but significant cause of precocious puberty (PP). The possibility of neoplasms should always be considered early to avoid delayed cancer diagnosis and treatment in cases of PP.