Myositis ossificans (MO) may be included in the group of lesions described as pseudosarcomas. Its clinical and histological picture frequently mimics a malignant neoplasm and therefore, ultimate diagnosis and implementation of adequate treatment requires the cooperation of interdisciplinary team of physicians. The paper presents the case of 20-year old female patient suffering from severe pain in the right thigh. The patient was initially diagnosed with the lower limb overload. Rest and administration of non-steroidal anti-inflammatory drugs (NSAID) were recommended. Due to the lack of the efficacy of the recommended conservative treatment and detection of tumorous mass on ultrasound examination, the patient was referred to the cancer centre. The diagnostic procedures were extended and an open biopsy of the lesion was performed which revealed the presence of MO. The patient underwent a surgical procedure during which the pathological mass was entirely removed. Follow up examinations conducted upon the conclusion of the rehabilitation indicate no pathologies in the operated area.