Juvenile dermatomyositis is a common inflammatory muscle disease of childhood, characterized by weakness in proximal muscles and specific skin rash. In case of juvenile dermatomyositis without characteristic clinical features, non-invasive imaging tools such as $^{99m}Tc$-HDP three-phase bone scan are very helpful in diagnostic workup of myopathies. We report a case of 13-year old female with juvenile dermatomyositis, in which $^{99m}Tc$-HDP three-phase bone scan was useful in diagnosis and assessing therapy response.