Neuroblastoma has been recognized as the most common solid tumor of infancy and childhood. The occurrence of bilateral adrenal neuroblastoma, however, is extremely rare and only a small number of cases have been previously reported. The authors herein report the clinical, histopathological and molecular biological features of two bilateral adrenal cases out of 125 neuroblastoma patients treated at Kyushu University Hospital over a 35-year period. The clinical and histopathological data of the two cases of bilateral adrenal neuroblastoma were reviewed. In Case 1, which had multiple liver metastases, a post-mortem examination revealed bilateral adrenal involvement. In Case 2, which had been detected by mass screening, CT showed masses in both adrenal glands. No big differences in size were recognized between the tumors in either of the cases. A histopathological examination revealed rosette fibrillary type neuroblastomas in both cases. The DNA of these tumor samples stored at -80 degrees C was extracted and the number of copies of the N-myc gene was determined by a Southern blot analysis. Fourteen copies of the gene were detected in Case 1, whereas neither of the tumors in Case 2 showed any amplification. The clinical outcome, histopathological findings and N-myc gene analysis of two cases might support the variety of biological features of this rare group of neuroblastoma.