This is a longitudinal cephalometric study of patients with craniofacial synostosis (Crouzon's and Apert's) syndromes who underwent Le Fort III advancement during early childhood. The objectives of the study were to quantify presurgical growth, surgical results, and surgical stability as well as long-term postsurgical growth. Of the 31 patients operated on during their growth period (less than 10 years of age), 17 had sufficient records to be included in the study: at infancy, before the Le Fort III osteotomy (average age=7.3 years, range: 4.8-10 years), and immediately after surgery. Ten of the patients were followed radiographically long term for an average of 6.1+/-2.7 years (range: 4.5-10.8 years). The presurgical abnormal midfacial vertical growth pattern was accurately described with a progressive class III discrepancy and an increasing exophthalmos. Remarkable postoperative stability of the maxillary segment was observed. After surgery, growth of the midface was measured, together with minimal, if any, anterior growth, similar to the presurgical growth pattern and rate. No actual detrimental or beneficial effect of surgery on subsequent growth was seen. This study quantitatively confirms that the standard Le Fort III osteotomy is a stable and effective but generally not definitive procedure in childhood. This study might also serve as a control sample to compare with groups of patients undergoing distraction osteogenesis to verify the actual advantages and shortcomings of this alternative technique.