Because neuroblastoma is predominantly a tumor of childhood, patholgists and clinicians tend to exclude it from differential diagnosis when the patient is an adult. The diagnosis of neuroblastoma by light microscopy can be difficult because of similarities between neuroblasts and cells of other round cell neoplasms. The fine structural features of neuroblastoma is distinctive and is valuable in its diagnosis. We present 2 cases of neuroblastoma and a case of ganglioneuroblastoma arising in adults with their ultrastructural findings.