The olfactory system is damaged to varying degree in the presence of clinically evident Parkinsonism. This chapter focuses on idiopathic Parkinson's disease (IPD) and familial Parkinsonism, as well as the known variants, Guam PD-dementia complex; Lewy body disease (LBD); multiple system atrophy (MSA), progressive supranuclear palsy (PSP), cortico-basal degeneration (CBD), drug induced PD (DIPD), vascular Parkinsonism (VP) and X-linked dystonia-Parkinsonism ('Lubag'). Patients with IPD have a profound disorder of olfactory function. This observation is based on pathological abnormality, psychophysical tests and evoked potential studies. Normal olfaction would favour essential tremor with the proviso that females with tremor-dominant IPD might also have a normal result. Degenerative syndromes with smell impairment may be split into two major categories that is, IPD, LBD, MSA where there is disorder of α-synuclein (alpha-synucleinopathy) and those with more normal olfaction that is, Alzheimer's disease, CBD and PSP where there is disorder of tau protein (tauopathy).