We investigated the incidence and extent of Lewy body (LB)-related alpha-synucleinopathy (LBAS) in the olfactory bulb (OB) in 320 consecutive autopsy patients from a general geriatric hospital (mean age, 81.5 +/- 8.5 years). Paraffin sections were immunostained with anti-phosphorylated alpha-synuclein, tyrosine hydroxylase, phosphorylated tau, and amyloid beta antibodies. LBAS was found in 102 patients (31.9%) in the central nervous system, including the spinal cord; the OB was involved in 85 (26.6%). Among these 85 patients, 2 had LBAS only in the anterior olfactory nucleus, 14 in the peripheral OB only, and 69 in both areas. In 5 patients, Lewy bodies were found only in the OB by hematoxylin and eosin stain; 3 of these patients had Alzheimer disease, and all had LBAS. Very few tyrosine hydroxylase-immunoreactive periglomerular cells exhibited LBAS. All 35 LBAS patients with pigmentation loss in the substantia nigra had LBAS in the OB. LBAS in the amygdala was more strongly correlated with LBAS in the anterior olfactory nucleus than with that in the OB periphery. LBAS did not correlate with systemic tauopathy or amyloid beta amyloidosis. These results indicate a high incidence of LBAS in the aging human OB; they also suggest that LBAS extends from the periphery to the anterior olfactory nucleus and results in clinical manifestations of LB disease.