The growth capacity of the vomero-premaxillary suture (VPS) was analysed as this growth site, sometimes exposed during cleft surgery, is usually unrecognized in the patient's mid-facial development. Metallic implants were inserted on both sides of the suture in eight infants with unilateral cleft lip and palate at the time of the first surgery. The patients were followed roentgencephalometrically to the age of three years. Growth between the vomer and premaxilla was recorded in every case, with growth being especially marked during the first year of life. The horizontal increment of growth between the pins was greater than the vertical increment. On the basis of these findings, it was proposed that surgery which seriously impedes or stops growth in the VPS is likely to be an important factor in the etiology of the mid-facial retrusion that is sometimes seen in patients with unilateral cleft lip and palate.