BACKGROUND: Prenatally diagnosed neuroblastomas have been reported in increasing numbers over the past several years, and there are now a few reviews based on up to 21 cases. The purpose of this article is to review the clinical and biologic features of prenatally diagnosed neuroblastoma based on a review of 55 cases. METHODS: A review was conducted of 3 cases seen at the study institution and 52 other cases reported thus far in the literature. RESULTS: Prenatal diagnosis was made usually after 32 weeks of gestation. Approximately 93% of the tumors were adrenal in origin, and 44% of these were cystic. Thirty-seven patients (67%) had Stage I disease, 12 (22%) had Stage IV-S disease, and only 3 (5%) had Stage IV disease. The DNA index was favorable (> 1) in 14 of 16 patients studied. None of these 16 patients studied had amplification of the N-myc oncogene. Catecholamines were elevated in only 33% of the patients. The liver was the most common site of dissemination, which was observed in 25% of patients; bone involvement was not observed in any patient. Ultrasonography failed to detect existing hepatic metastasis in three patients. Primary surgical resection was performed in 47 patients (85%). Chemotherapy was given to five patients and radiotherapy to three. Of the 50 patients for whom follow-up information was available, 45 (90%) were alive at a range of 2-120 months from diagnosis. CONCLUSIONS: Prenatally diagnosed neuroblastomas are predominantly adrenal in origin and frequently cystic. The liver is the most common site of dissemination and bone involvement is notably absent. The vast majority of these infants have a favorable stage of disease (I, II, and IV-S) and favorable biologic features, and consequently have an excellent prognosis. Although surgery alone is curative for most patients, a period of observation may avoid surgery in some individuals who may achieve spontaneous regression.