Two cases of fibrous dysplasia in the skull base bone appeared hypointense on T 1 -and T 2 -weighted magnetic resonance imaging, with accumulation of [ 11 C]methyl-L-methionine ([ 11 C]Met) on positron emission tomography (PET). Fibrous dysplasia is a benign bone disorder which is identified by its distinctive radiography, computed tomography, and bone scintigraphy findings. [ 11 C]Met PET may indicate the presence of viable tumor-like cells in fibrous dysplasia.