The place of surgical treatment in obstructive sleep apnea syndrome (OSAS) remains unclear. Uvulopalatopharyngoplasty (UPPP) has a response rate of 41% overall and only 5% when retrolingual narrowing is present. Thus, in cases with suspected hypopharyngeal collapse maxillofacial surgery has been proposed with improved results. The Stanford group has designed a step-by-step surgical procedure tailored to the specific anatomical abnormalities encountered in each patient. The goal is to avoid a full maxillomandibular advancement osteotomy (MMO), at least in a subgroup of patients, beginning with a limited mandibular osteotomy (with or without hyoid myotomy and hyothyroidopexy and with or without UPPP) (phase 1 surgery). In this procedure MMO is performed as the second or third step (phase 2 surgery). The present study reports on our prospective experience with 51 consecutive patients (64 surgical procedures) treated by the step-by-step maxillofacial surgery previously described by the Stanford team. Only 2 of the 53 patients initially treated were lost for follow-up. Surgery was considered a success if the postoperative apnea and hypopnea index (AHI) was less than 15/h with at least a 50% reduction. Forty-four patients had phase 1 surgery. The success rate was 22.7% (10 of 44). The mean AHI was unchanged with a trend for reduction in the apnea index. Twenty patients had maxillomandibular advancement surgery (phase 2) (13 failures of phase 1, 7 patients primarily because of facioskeletal deformities). The AHI decreased from 59 +/- 29/h to 11 +/- 9/h after phase 2. Of the patients 75% (15 of 20) were considered to have had a successful outcome. In conclusion, phase 1 does not seem effective in most patients with OSAS. The results of phase 2 surgery are successful in young patients with severe OSAS even if the surgical technique is more aggressive.