The study aimed to compare olfactory function in idiopathic Parkinson's disease (IPD) and nonidiopathic Parkinson's syndrome (PS). At their first visit 50 PS patients (age 38-80 years) received testing for odor threshold, olfactory discrimination and identification. All patients underwent extensive neurological diagnostics including PET scans. Patients were followed up for 6-12 months. Most of IPD patients were functionally anosmic (n = 19), the remaining IPD patients had severe/moderate hyposmia (n = 18). PS patients diagnosed with multiple system atrophy had less severe olfactory deficits Q hyposmia, 1 normosmia). With the exception of 1 hyposmic patient, other PS patients had no olfactory deficits (progressive supranuclear palsy, corticobasal degeneration, psychogenic PS, essential tremor). This study added to previous findings: (1) there was no major difference betwesen olfactory function in IPD subtypes; (2) all olfactory tests differentiated IPD from nonIPD. These data suggest that olfactory probes improve the diagnostic armamentarium in IPD. (C) 2002 Published by Elsevier Science Ltd.