Fifty four patients with a single parenchymal brain cysticercus in the acute encephalitic phase were studied to outline the features of this form of the disease. Seizures were the presenting symptom in all cases. Twenty six patients had a single seizure and 28 had several seizures before admission. Neurological examination was normal in 45 patients and showed focal signs in nine. All patients had a single enhancing CT lesion; all but three lesions were < 20 mm. Anticonvulsants were started in every patient. Forty five patients were followed up for 18 (SD 6) months. Thirty seven of these 45 patients received albendazole. Four weeks after the trial, CT showed resolution of lesions in all cases. The remaining eight patients refused albendazole, and CT showed persistence of lesions by 16 weeks in six cases. At the end of the follow up, all patients who received albendazole were free of seizures as opposed to three of eight patients who did not receive the drug. Focal signs improved in the nine patients with these signs (all received albendazole). Recognition of this form of neurocysticercosis permits early treatment with albendazole that greatly improves the prognosis.