Our purpose was to sonographically demonstrate the femoral heads of two infants with proximal focal femoral deficiency (PFFD) and to classify PFFD with the contribution of ultrasonography (US). On the radiograph of Case 1, a seven-month-old male with a short right thigh, there was marked hypoplasia of the proximal half of the right femur. Ipsilateral acetabulum was dysplastic. On the US, the femoral head was hypoplastic. On the radiograph of Case 2, a 16-day-old male with a short right thigh, the right femur was shorter and thinner than the left femur. An adequate ipsilateral acetabulum was found. US revealed a normal femoral head. US helped the classification of Case 1 as Aitken class C and Case 2 as and Aitken class A, by demonstrating the status of cartilaginous femoral heads in PFFD. Combined with radiography, US can be used in the classification of PFFD and in the evaluation of the unaffected hip.