Photosensitivity is the most common mode of seizure precipitation. It is age-related, more frequent in females, and most often found in generalised epilepsies. Little is known about its relation to individual epileptic syndromes. This study on 1062 epileptic patients who had 4007 split screen video EEG investigations revealed that the relation to generalised epilepsy is even more close than generally believed. Versive seizures with visual hallucinations was the only focal seizure type related to photosensitivity. Of the syndromes of generalised epilepsy, only childhood absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with grand mal on awakening were related to photosensitivity. The closest correlation was with juvenile myoclonic epilepsy. This is confirmed by a relation to the poly-spike wave pattern, and by an increase of myoclonic seizures by intermittent light stimuli. No relation was found with early childhood syndromes of generalised epilepsy, or generalised tonic-clonic seizures in the evening, or, most remarkably, with juvenile absence epilepsy. In generalised epilepsies with onset around puberty, photosensitivity could thus act as a pathoplastic factor. The female preponderance in both childhood absences and photosensitivity could be due to the same unknown factor.