We report a boy with dysplasia epiphysealis hemimelica of the knee, particularly emphasizing MRI findings. When he was 14 months of age, plain radiography exhibiting juxta-articular soft tissue mass with small, punctate, calcified foci did not warrant the definitive diagnosis, while MRI clearly demonstrated osteocartilaginous overgrowth of the femoral epiphysis. The epiphyseal mass mostly showed the same signal intensity as normal cartilage but contained low signal spots corresponding to calcified foci. The cartilaginous cap was depicted as a mottled area of high intensity on a T2-weighted image. When the patient was 4 years of age, this ossified mass was resected surgically and pathologically identified as osteochondroma incorporated into the epiphysis.