Objectives: The prenatal finding of a large cystic adrenal mass raises the dilemma of the differential diagnosis between adrenal hemorrhage and cystic neuroblastoma. The possibility of a neuroblastoma usually leads to surgical excision of such tumors. Nevertheless, an adrenal hemorrhage has to be recognized, so that unnecessary surgery may be avoided. Methods: Three cases of large prenatally detected adrenal masses managed nonoperatively are reported. Data studied were: age at the diagnosis, prenatal and postnatal ultrasonographic consistency, and tumor marker levels. Size and sonographic evolution were also studied. Results: In all 3 cases, a cystic mass, measuring more than 40 mm in size, was detected during the 3rd trimester of pregnancy. The sonographic appearance evolved from a sonolucent tumor to a heterogeneous mass with hyperechoic areas. The tumor marker levels were normal. All infants had a documented decrease in mass size at birth and were managed nonoperatively. All these tumors were considered adrenal hemorrhages. Conclusions: Prenatal ultrasonography rarely permits to distinguish an adrenal hemorrhage from a cystic neuroblastoma. The differential diagnosis, even in large masses, is based on close postnatal follow-up with serial sonography. Surgery is not mandatory, unless the size does not decrease. However, without pathologic proof, it is not possible to differentiate an adrenal hemorrhage from a spontaneously resolved neuroblastoma.