The purpose of this study was to determine the incidence and degree of sagittal plane deformity that occurs during limb lengthening of the femur. Twenty-one patients (25 limbs) were identified who underwent femoral lengthening. The limbs were lengthened a mean of 6.1 cm, and mean follow-up was 1.5 years. The immediate postoperative deformity in the sagittal plane was 8.3°; this deformity did not progress during lengthening (P<.05). Mean displacement in the sagittal plane was 3.1 mm.Angular deformities, although typically small, can occur in the sagittal plane and may be accompanied by displacement. These deformities are usually present immediately postoperatively and typically do not worsen significantly with lengthening.