The computed tomography (CT) and ultrasound (US) imaging studies were performed on skeletal muscles of two siblings (5-year-old boy and 10-year-old girl) with central core disease. The appearance of low-density areas in muscles was remarkable at the levels of the 3rd lumbar vertebra (L3), the midthigh and the thickest part of legs. The muscles at the levels of L3 and thigh were more severely affected than those of legs. Especially, paravertebral muscles, m. vastus, m. sartorius, m. gracilis tended to be more severely affected. The muscles of the legs except m. soleus were well preserved. US imaging of the thigh revealed a marked increase of echogenicity of rectus muscle as well as opaque, indistinct changes of fascia and bone. In contrast, the CT finding of the rectus muscle was relatively well preserved.