Factors that determine a successful outcome following uvulopalatopharyngoplasty (UPPP) for obstructive sleep apnea (OSA) are not well defined. This study was undertaken to determine if prior tonsillectomy is predictive of a lower response rate to UPPP. A retrospective review of a cohort undergoing UPPP alone or in combination with nasal septoplasty for OSA was undertaken. Preoperative and postoperative polysomnograms were obtained to evaluate the severity of the OSA. The sample was a consecutive series of 79 patients with OSA. Clinical evaluation was performed by both an otolaryngologist and a pulmonologist. Surgical treatment in this group of 79 patients included 52 UPPP and 27 UPPP in patients with prior tonsillectomy. Concurrent septoplasty was undertaken in 17 patients. Criteria for outcome were based on comparison of preoperative and postoperative polysomnograms (i.e., apnea index, respiratory disturbance index change, and lowest saturation). A response to therapy was defined as a reduction in apnea index greater than 50%. A success was defined as apnea index less than 5, reduction of respiratory disturbance index greater than 50%, and nadir saturation greater than 82%. In 79 patients with OSA, 78% responded and 37% reflected therapeutic successes. Patients with history of prior tonsillectomy were less likely to have therapeutic improvement following UPPP. In 52 patients without previous tonsillectomy, 88% responded and 52% had a successful outcome. Of those with previous tonsillectomy, 59% responded and 7% had a successful outcome. The status of previous tonsillectomy is an important prognostic indicator in the success of UPPP for the treatment of OSA. We speculate that the presence of palatine tonsils allows the removal of an extra measure of oropharyngeal tissue, thereby improving the likelihood of success for UPPP.