Recent data suggest that cholesterol metabolism is linked to susceptibility to Alzheimer's disease (AD). However, no direct evidence has been reported linking cholesterol metabolism and the pathogenesis of AD. To test the hypothesis that amyloid β-peptide (Aβ) deposition can be modulated by diet-induced hypercholesterolemia, we used a transgenic-mouse model for AD amyloidosis and examined the effects of a high-fat/high-cholesterol diet on central nervous system (CNS) Aβ accumulation. Our data showed that diet-induced hypercholesterolemia resulted in significantly increased levels of formic acid-extractable Aβ peptides in the CNS. Furthermore, the levels of total Aβ were strongly correlated with the levels of both plasma and CNS total cholesterol. Biochemical analysis revealed that, compared with control, the hypercholesterolemic mice had significantly decreased levels of sAPPα and increased levels of C-terminal fragments (β-CTFs), suggesting alterations in amyloid precursor protein processing in response to hypercholesterolemia. Neuropathological analysis indicated that the hypercholesterolemic diet significantly increased β-amyloid load by increasing both deposit number and size. These data demonstrate that high dietary cholesterol increases Aβ accumulation and accelerates the AD-related pathology observed in this animal model. Thus, we propose that diet can be used to modulate the risk of developing AD.