SUMMARY In a group of forty cases of cysticercosis of the central nervous system, 59% presented with intracranial hypertension due to obstructive hydrocephalus. Ventricular or cistemal cysts, and chronic cysticercus meningitis were the most common causes of hydrocephalus. Seizures occurred in 40% of the patients, in one-half of them in association with CT-detected parenchymatous cysts. In 20% of the cases progressive mental deterioration was the main clinical feature, at times associated with hydrocephalus. CT scan provided the highest diagnostic yield, being abnormal in 90% of cases. Long term prognosis was poor, with a mortality rate of 38% over a 40-month follow-up period. The most common cause of death (60%) was meningitis. CSF shunting is the treatment of choice for hydrocephalus, irrespective of its mechanism. Surgical resection is indicated in some cases with a single superficial (cortical) or posterior fossa cyst. Supratentorial cysts carry a relatively benign prognosis.The aetiology of neurocysticercosis, the biological cycle of the parasite, and the pathological lesions it provokes have been well documented.'-'°However, some aspects of the disease, such as its initial clinical manifestations, the yield of various diagnostic methods, and its treatment still remain unclear. In addition, accurate figures on outcome and long-term prognosis are not widely available. We report a group of 40 patients with cysticercosis of the central nervous system, in an attempt to clarify these questions.Forty patients with a diagnosis of neurocysticercosis were studied. Aids to diagnosis included complement fixation reaction in blood and cerebrospinal fluid (CSF), counterimmunoelectrophoresis, and intradermal reactions. These tests were positive in 32 cases. The diagnosis was verified pathologically in 18 cases, and the cause of death was verified by necropsy in 10 cases. Follow-up covered periods from 7 to 97 months (mean: 40 months) in 32 patients.