Myositis ossificans (MO) also defined as myosteosis or hematoma ossificans, is a benign condition presenting as an heterotopic, well- defined neoformation in muscles and soft tissues. It was first described by Guy Patyn in 1692 and defined in its histopathological aspects by Von Dusch in 1868. It most frequently has a post-traumatic onset (60-75% of cases), usually following small repeated traumas or a single bruising episode. MO is rare in subjects under 10 years of age, whereas it is more frequent in teen-age athletes, and over 50% of cases are diagnosed in the third decade of life. Its etiopathogenesis in unknown, although it is associated with a traumatic event in 75% of cases. MO most common localizations are arms, legs, shoulders and hands, rarely chest. The lesion presents with different degrees of maturation and diagnostic tools are echotomography (ECT) as a primary investigation, and NMR for a better diagnostic assessment. Because of the self-limiting nature of the lesion and its spontaneous resolution, a conservative treatment is advised along with radiological follow-up which is most indicated in the presence of either typical MO features or highly suggestive ECT o NMR findings. In case of uncertain diagnosis, relevant muscular function impairment, considerable lesion dimension or severe pain, exeresis and histological examinations are suggested. The present paper describes and discusses a clinical case of MO in a child, with a rare localization.