Alzheimer's disease (AD) is neuropathologically characterized by the presence of senile plaques. The formation of these plaques is caused by the accumulation of amyloid-beta protein (Aβ), a process that begins decades before the onset of the first clinical symptoms. Senile plaques can be visualized by using positron emission tomography (PET) and the tracer 11C-PIB. Such 'amyloid imaging' can contribute significantly to both early and differential diagnosis of Alzheimer's disease. In the future, amyloid imaging could also be useful for selecting patients for clinical trials and in evaluating the effects of disease modifying agents tailored at lowering Aβ burden.