Osteochondromas are the most common benign tumours of the bone. They are solitary or multiple, pedunculated or sessile exophytic outgrowths from the bone surface that are composed of cortical and medullary component with an overlying hyaline cartilage cap. Marrow and cortical continuity with the underlying parent bone is the characteristic of the lesion; they mostly arise from the metaphysis of the bone. Osteochondromas arising from the diaphysis are rare; and nerve palsy arising in the setting of a diaphyseal osteochondroma is even rarer. This is a report of solitary osteochondroma arising from diaphysis of left humerus in a 10 years old boy, which resulted in median nerve palsy. Surgical excision relieved the symptoms completely. The aim of this case report was to draw attention to an unusual etiology of median nerve palsy caused by an osteochondroma arising from the diaphysis of humerus which is a rare site, and to emphasize its importance.