Ninety-seven limbs, in eighty-one patients, with a diagnosis of congenital deficiency of the fibula have been reviewed. A classification was devised to distinguish the minimal hypoplasia of the fibula (Type I) from the well-known complete absence (Type II). Congenital anomalies of the femur were present in 76 per cent of patients with Type I deficiency and in 59 per cent with Type II. The shortening of the limb was by 13 per cent in Type I and by 19 per cent in Type II, and the percentage shortening was fairly constant during growth. A detailed description of the spectrum of other congenital anomalies was found to be characteristic: for example, the ball and socket formation of the ankle, tarsal coalition and anomalies of the foot. The treatment aimed simply to equalise leg length in Type I deficiency, while amputation of the foot and the fitting of a prosthesis were necessary in Type II to obtain satisfactory function.