Background: We carried out a clinical and electroencephalographic (EEG) study to reveal the pathophysiology of acute symptoms elicited by a TV animation program. Methods: Clinical data and EEG were obtained from 20 patients ranging in age from 6 to 30 years. A pattern presentation and an intermittent photic stimulation were performed. Results: Of 20 patients, 13 had a convulsion and seven had other symptoms, mainly nausea and/or vomiting. A photoparoxysmal response (PPR) was confirmed in 12 of 13 patients (92.3%) who had a convulsion. Only one of seven patients (14.3%) without a convulsion showed a PPR. The incidence of PPR was significantly higher in patients with convulsion than those without convulsion. There were no significant differences in the family history of convulsion, gender, parameters associated with TV watching and basic EEG between the two groups. All patients with PPR had a convulsion or consciousness disturbance. Conclusion: Acute symptoms, such as convulsion and impairment of consciousness, are supposed to be based on photosensitivity. © 1998 Wiley. All rights reserved.