A new study provides strong evidence associating seizures with areas of brain tissue swelling in people infected by a parasitic tapeworm. The swellings, called perilesional edemas, form around dead, calcified cysts that result when larvae of Taenia solium tapeworms lodge in the brain. The illness caused by T. solium infection — neurocysticercosis — is the most common cause of adult-onset seizures and epilepsy in developing countries where the tapeworm is endemic.