In a photosensitive patient intermittent photic stimulation (IPS) accidentally provoked a generalized tonic-clonic seizure during simultaneous recordings of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Before seizure onset, IPS consistently induced generalized photoparoxysmal responses (PPRs). These PPRs were associated with increases in blood oxygen level dependent (BOLD) signal in the visual cortex, the thalamus, and both superior colliculi, and a decrease in BOLD signal in the frontoparietal areas. The BOLD signal in the visual cortex increased in magnitude during consecutive epochs of IPS associated with PPRs. We propose that repeated IPS led to an excessive amount of neuronal activity in the visual cortex that evoked PPRs and finally exceeded a critical threshold and triggered a generalized seizure.