The term proximal focal femoral deficiency (PFFD) is applied to a spectrum of conditions characterized by partial absence and shortening of the proximal femora and thought to result from an early disturbance of growing mesenchyme. The mildest cases, Classes A and B, exhibit a relatively normal acetabulum and capital femoral epiphysis, despite the dysplastic shaft. There may be a subtrochanteric varus deformity or a pseudoarthrosis accompanying the shortening of the femoral shaft. At the opposite end of the spectrum, the most severely deformed cases, Classes C and D, have involvement of the acetabulum, and the entire proximal femur. In cases of advanced dysgenesis, the findings include: a stunted severely shortened femur with a club-shaped or pointed proximal end, an iliac projection just above the anatomic site of the acetabulum, a spherical obturator foramen, and squaring of the iliac crest. Twenty-one patients (2 bilateral) with proximal focal femoral deficiency are presented (23 femurs). Differentiation of proximal focal femoral deficiency from other congenital and acquired deformities of the hip joint is essential for selecting the proper treatment.