INTRODUCTION. West Syndrome involves epileptic encephalopathy in infants, occurring with an incidence of 5/10000 live births. Its main clinical feature are spasms that occur in clusters, which are associated with an EEG pattern called hypsarrhythmia and psychomotor retardation in most patients. West Syndrome is associated with many underlying conditions and the terms idiopathic, cryptogenic, and symptomatic are used for its aetiological subgroups. OBJECTIVE. The objective of this investigation was to determine the aetiological diagnosis of patients with West Syndrome and to compare the results with other studies. METHOD. In this 34-year longitudinal prospective one-centre study, 404 patients were studied. All patients exhibiting the diagnostic criteria for West Syndrome were investigated by clinical and neurological examination, EEG, ophthalmologic, psychological, metabolic, genetic, as well as neuroradiological methods, according to their particular indications. RESULTS. 36 (8.9%) patients had normal development, in whom infantile spasms occurred without any identifiable underlying cause, forming the idiopathic group. 51 patients (12.6%) with neurological impairment of unknown aetiology formed the cryptogenic group. The greatest number of patients (317 or 78.5%) formed the symptomatic group, in which neurological features and developmental delay preceded the onset of spasms. Disgenetic disorders and hereditary metabolic diseases were aetiological factors 44 (10.8%) patients. Prenatal and perinatal aetiological factors were revealed in one third of the patients (134 or 31%). Postnatal aetiological factors were revealed in 42 (10.2%) patients. In our study, disgenetic disorders were registered less frequently and perinatal complications more frequently than in other studies. CONCLUSION. Our results indicate the possibility of preventing West Syndrome with good quality obstetric and neonatal care, as well as the early prenatal diagnosis of brain malformations. Modern, sophisticated investigation makes the more accurate aetiological diagnosis of West Syndrome possible.