Interictal EEG records of Nigerian epileptic patients living in Lagos and clearly diagnosed as having grand mal epilepsy were compared with those of British epileptic patients with a similar diagnosis. Interictal EEG abnormalities (spike and wave discharges, (SW), photoparoxysmal discharges (PPD), and nonspecific changes) were significantly less common in Nigerian patients (incidence 15.7%) compared with British patients (incidence 52.9%) irrespective of age or sex of the patients. These findings may be related to ethnic or geographical factors. Rarity of PPD in Africans has previously been attributed to ethnic factors. Other studies have demonstrated an influence of geographical factors, specifically sunshine. In papio papio, such a geographical factor was shown to influence occurrence of PPD. In human epileptic subjects, environmental sunshine has been found to inversely influence the occurrence of PPD as well as SW. Besides possible ethnic factors, the relative rarity of interictal EEG abnormalities in Africans with grand mal epilepsy may be related to the larger amount of sunshine in the tropics.