Perimesencephalic subarachnoid hemorrhage (PM‐SAH) refers to intracranial hemorrhage located in the perimesencephalic cistern. The etiology remains mainly unclear, although venous leakage or rupture has been postulated. We report an interesting case of a 57‐year‐old healthy man who presented initially with PM‐SAH with worsening of subcortical lesions on follow‐up neuroimaging. Histopathological examination demonstrated cerebral amyloid angiopathy with perivascular inflammation.