Résumé : We demonstrate label-free imaging of cerebral $beta$-amyloidosis ex vivo and in a living mouse model of Alzheimer's disease using extended-focus Fourier domain optical coherence microscopy (xfOCM). xfOCM provides 3D, high-resolution images of individual $beta$-amyloid plaques in the brain parenchyma and vasculature and requires no staining of the Alzheimeric sample under investigation. xfOCM also opens the possibility to perform minimally invasive studies of $beta$-amyloid pathology in vivo, without the use of labeling methods, which potentially confound experimental findings.