Among three recognised clinical phenotypes, type 3a Gaucher's disease is characterised by mild to severe systemic disease, neurological manifestations and myoclonic seizures. We report the long term clinical and electrophysiological follow-up of a 27-year old man with a diagnosis of type 3a Gaucher's disease, which was confirmed by bone marrow biopsy examination and leukocyte glucocerebrosidase level measurement. His neurological examination was normal throughout the follow-up period. EEG examination, recorded five days after the first seizure, revealed generalised nonrhythmic paroxysmal rapid spikes with occipital predominance increased by photic stimulation and normal background activity. The frequency of seizures increased from 3-4/year to 1-2/month within a follow-up period of 12 years and a repeat EEG examination on the eight year of diagnosis revealed additional background slowing. A giant potential was obtained in somatosensory evoked potential (SEP) examination. EEG findings of this case demonstrate a specific pattern with rapid spike activity, photosensitivity, eye closure sensitivity and gradual background slowing. (C) 2000 BEA Trading Ltd.