A case of pericapsular desmoid tumor is presented. The MR features of signal hypointensity and association with the joint capsule suggested the diagnosis of focal PVNS or giant cell tumor of tendon sheath. Arguing against the diagnosis of PVNS were the absence of significant joint effusion, the unifocality of a fairly large lesion, and the absence of bony erosion. While nonspecific, the MR features in some cases of desmoid tumor may help to suggest the correct diagnosis.