Brazil has the world's highest incidence of adrenal cortex tumor in childhood, mainly in Parana and Sao Paulo states. The diagnosis in children is done by the signs and symptoms secondary to the production of adrenal cortex hormones. The occurrence of polycythemia in patients with adrenal cancer is very rare, especially in children. The authors describe a case of adrenal cortex tumor in a child diagnosed during investigation of polycythemia. In the case described, the polycythemia was justified by increased production of erythropoietin.