Periosteal chondroma is a slow growing benign cartilaginous tumor of bone. It is rarely reported among Thai people. The authors present a case of periosteal chondroma of the proximal humerus. A 14-yearold girl was admitted with a painless mass around her left shoulder.
On magnetic resonance images, a subcutaneous lesion with hypointensity on T1-weighted images and marked hyperintensity on T2-weighted images, eroded the underlying cortical bone of the proximal humerus. The patient underwent marginal excision. There was no recurrence of the lesion during 3 years of follow-up.

Keywords: Periosteal chondroma, Chondroma, Humerus