The spontaneous pseudoseizures resembling tonic-clonic seizures in 25 patients were recorded on simultaneous videotape and electroencephalograms and were compared with the seizures recorded from 25 patients with true tonic-clonic epileptic events. The goal of the comparison was to identify bedside clinical criteria to assist in differentiating between the two groups. The variables of age, sex, and selected physical manifestations of the events were compared for the two groups by appropriate statistical methods, including a multivariate step-wise discriminate analysis. Significant differences between the two groups of seizures were identified for several variables, and most strikingly for the character of upper and lower extremity movements, the time of vocalization during the event, the character of pelvic movements, and the nature of body tone during the events. Useful bedside criteria for distinguishing a pseudoseizure from a tonic-clonic seizure were identified.