Two cases of intra-articular development of an osteochondroma in the proximal epiphysis of the tibia are reported. The first case, a 3 year old boy, resulted in blocking of the knee. After resection of the mass the diagnosis was confirmed by pathology. The second patient, an 8 year old boy, had no symptoms and surgery was not performed, although ablation was required of an associated astragalian osteochondroma of tibiotarsal intra-articular development. Relations between these epiphyseal osteochondromata and hemimelic epiphyseal dysplasia and metachondromatosis are discussed.