OBJECTIVES--To define the clinical characteristics of a group of patients with startle provoked epileptic seizures (SPES). METHODS--Nineteen patients were identified during the course of a larger study of clinical seizure patterns. A witnessed seizure account was obtained in all patients; interictal EEG in 18, video-EEG-telemetry in eight, CT in 18, and high resolution MRI in eight. RESULTS--The onset of SPES was in childhood or adolescence in 14 of 19 patients. It was preceded by exclusively spontaneous seizures in nine patients and SPES had been replaced by exclusively spontaneous seizures in two patients. Sudden noise was the main triggering stimulus and somatosensory and visual stimuli were also effective in some patients. The clinical seizure pattern involved asymmetric tonic posturing in 16 of 19 patients. Focal neurological signs were present in nine patients, mental retardation in six, and 10 were clinically normal. Ictal scalp EEG showed a clear seizure discharge in only one patient with a tonic seizure pattern; over the lateral frontal electrodes contralateral to the posturing limbs. Brain CT showed a porencephalic cyst in three patients, focal frontal atrophy in one, and generalised atrophy in one. Brain MRI was undertaken in five normal subjects and three neurologically impaired patients, six with normal CT. It showed a porencephalic cyst in one patient. In six patients, there were dysplastic lesions. They affected the lateral premotor cortex in three patients and the perisylvian cortex in three patients, one with bilateral perisylvian abnormality. CONCLUSIONS--SPES are more frequent than is generally appreciated. They may be transient and occur relatively commonly without fixed deficit, by contrast with previous reports. The imaging abnormalities identified in those without diffuse cerebral damage suggest that SPES are often due to occult congenital lesions and that the lateral premotor and perisylvian cortices are important in this phenomenon.