OBJECTIVES/HYPOTHESIS: Orthonasal olfaction is severely altered in PD patients. Retronasal olfactory function has been shown to be preserved under certain conditions even in the absence of orthonasal function. This study was undertaken to investigate retronasal versus orthonasal olfactory function in Parkinson's disease (PD). STUDY DESIGN: Prospective study. METHODS: A total of 45 PD patients (mean age, 61 years; range 26-82 years) underwent orthonasal olfactory testing with a standardized olfactory test (Sniffin' Sticks) and retronasal olfactory testing with a 10-item identification kit based on aromatized powders. RESULTS: Regarding orthonasal tests, all PD patients scored within the range of hyposmia and functional anosmia. The mean correct orthonasal identification score for PD patients was 56% +/- 2.6%, and the mean retronasal identification rate was 60% +/- 3%. There was no significant difference between ortho- and retronasal odor identification (P = .15). CONCLUSIONS: The present study shows that retronasal and orthonasal olfactory function are severely impaired in PD patients, and this impairment is of similar magnitude for both functions. The contribution of this finding to the food-intake behavior of PD patients is discussed.