Active surveillance by virtually all electroencephalographic departments throughout Great Britain identified 118 patients who had a first seizure while playing an electronic screen game during two 3-month periods. Patients were divided into Group A (46 patients)--those for whom there was thought to be a definite causal relationship (type 4 photoparoxysmal response); Group B (25 patients)--those for whom there was a probable causal relationship (types 1-3 photoparoxysmal response, clinical evidence of photosensitivity, subsequent recurrent seizures on repeat exposure to electronic screen games, and/or occipital spikes in the resting electroencephalogram); and Group C (47 patients)--those for whom there was no apparent causal relationship. The number of patients in Group C did not exceed that expected by the chance occurrence of two common events (playing electronic screen games and incidence of epilepsy). Most (103/118) of the patients were in the age range of 7 to 19 years. Within this age group the annual incidence of first seizures triggered by playing electronic screen games (Groups A and B combined) was estimated to be 1.5/100,000.