Proximal femoral focal deficiency is a rare birth defect that affects the hip bone and the proximal femur. The incidence is one case per 50,000 to 200,000 population. The disorder may be unilateral or bilateral, with the hip being deformed and the leg shortened. The goal of treatment is to provide optimal function during standing and ambulation. A 15-year-old male diagnosed with left proximal femoral focal deficiency was admitted for prosthetic rehabilitation. He presented with a very short left lower extremity, 38 cm leg length discrepancy, flail left hip and knee joints, and normal range of motion at the left ankle, and with muscles graded at 4/5. The patient was independent in transfer activities and ambulated with bilateral axillary crutches. A combination of orthosis and prosthesis (henceforth "prosthosis") was designed for the patient with a mechanical hinge joint to equalize the leg length and to improve lower extremity function during standing and ambulation. Upon discharge, the patient was independent in donning and doffing the prosthesis, was ambulatory using the prosthesis without gait aid but with minimal listing during the stance phase on the prosthesis side. During the patient's two-year follow-up, adjustment of the prosthesis was done to accomodate growth; checking of the prosthesis for mechanical breakdown and anticipatory management of potential musculoskeletal complications and psychosocial concerns on the use of the prosthesis were also done.