Objectives Electronic dance music (EDM) concerts are becoming increasingly popular. Strong stroboscopic light effects are commonly part of these shows, and may provoke seizures in individuals with photosensitive epilepsy. This study aims to examine the risk of epileptic seizures during EDM concerts. Setting 28 EDM concerts taking place in The Netherlands. Participants We describe a young man who experienced a seizure during an EDM concert, and who later showed a positive electroencephalographic provocation test during exposure to video footage of the same concert. Subsequently, we performed a cohort study of 400 343 visitors to EDM concerts, divided in those exposed (concert occurring in darkness) versus unexposed (concert in daylight) to stroboscopic light effects. Results In total, 400 343 EDM concert visitors were included: 241 543 (representing 2 222 196 person hours) in the exposed group and 158 800 (representing 2 334 360 person hours) in the control group. The incidence density ratio of epileptic seizures in exposed versus unexposed individuals was 3.5 (95% CI: 1.7 to 7.8; p<0.0005). Less than one-third of cases occurred during use of ecstasy or similar stimulant drugs. Conclusion Stroboscopic light effects during EDM concerts occurring in darkness probably more than triple the risk of epileptic seizures. Concert organisers and audience should warn against the risk of seizures and promote precautionary measures in susceptible individuals.