Von Recklinghausen's neurofibromatosis is an autosomal dominant disease involving peripheral nerves and central nervous system. Obstructive hydrocephalus in this disease represents a common finding when it is due to the development of infratentorial neoplasm. Nevertheless, the occurrence of isolated nonneoplastic aqueductal stenosis in patients affected by neurofibromatosis has been described rarely. The authors report two cases of primary nontumoral aqueductal stenosis associated with Von Recklinghausen's disease who were diagnosed by CT scan and MRI. The pathogenesis of aqueductal narrowing in neurofibromatosis is discussed.