Summary: The high intensity sweetener aspartame has been implicated anecdotally in seizure provocation. This possibility was investigated with a randomized, double-blind, placebo-controlled, cross-over study. After an extensive search, 18 individuals (16 adults and 2 children) who had seizures allegedly related to aspartame consumption were admitted to adult or pediatric epilepsy monitoring units where their EEG was monitored continuously for 5 days. Aspartame (50 mg/kg) or identically enpackaged placebo was administered in divided doses at 800, 1000, and 1200 h on study days 2 and 4. All meals were uniformly standardized on treatment days. No clin-ical seizures or other adverse experiences were observed after aspartame ingestion. Mean plasma phenylalanine (Phe) concentrations increased significantly after aspar-tame ingestion (83.6 pIM) as compared with placebo (52.3 μCM).Results suggest that aspartame, in acute dosage of ε50 mg/kg, is no more likely than placebo to cause seizures in individuals who reported that their seizures were provoked by aspartame consumption.