The purpose of this study was to describe the natural history of untreated cysticercosis as monitored by cranial computed tomography (CT) and correlate it when possible with the pathologic stage of the disease noted at surgery. Serial CT was performed in 113 patients; two to four scans were obtained in each patient. Correlation with surgical specimens and clinical presentation is given. In the early, acute stage, focal nonenhancing areas of edema progress to homogeneously enhancing lesions. In the chronic phase, beginning a few months after infestation, nonenhancing cysts are seen, which later demonstrate ring enhancement. Lesions may then completely resolve or may resolve only to appear later as punctate calcifications. This radiologic progression suggests the need to reevaluate current concepts in therapy and diagnosis of this disorder. Studies on therapeutic efficacy should be based on both the improvement of clinical symptoms and evidence of lesion regression at CT.