Juvenile dermatomyositis (JDM) is a rare autoimmune disease characterized by inflammation of the muscle, connective tissue, skin, gastrointestinal tract and small nerves. Periorbital and facial edema may also be associated. Although localized edema is a common feature of juvenile dermatomyositis, generalized edema has been reported rarely. In this article, we report a 14-year-old boy with juvenile dermatomyositis presenting with generalized edema. Of the diagnostic criteria of JDM, severe symmetric weakness of the proximal musculature, characteristic cutaneous changes, elevated serum muscle enzymes and myopathic electromyographic abnormalities were observed. Magnetic resonance imaging (MRI) of the lower extremities and pelvis showed marked diffuse edema in the subcutaneous tissue, muscles and myofascia. We suggest that MRI findings, which are not among the diagnostic criteria, may also be included in the diagnostic criteria of JDM. To the best of our knowledge, this is the 19th case of JDM reported for generalized edema in the English literature.