Purpose: Velopharyngeal (VP) functional outcomes were analyzed in 155 consecutive sphincter pharyngoplasties (SP) to determine the general efficacy and modulating variables for that operation in the treatment of patients with velopharyngeal dysfunction (VPD). Methods: A retrospective review of 155 consecutive patients undergoing SP at a tertiary cleft center between 1990 and 2000 was performed. 98% of the operations were performed by or directly supervised by one of two senior cleft surgeons using the Jackson modification of the Hynes SP. Each patient included in the analysis (n=155) underwent a standardized evaluation regimen including pre- and 3-month postoperative perceptual VP rating and videonasendoscopic (VNE) and videofluoroscopic VP functional evaluations. The perceptual ratings were performed by an experienced cleft team speech/language pathologist using a 0-5 severity scale to rate hypernasality (HN), nasal emission (NE), and nasal turbulence (NT). For endoscopic and fluoroscopic examinations, VP function was assessed by the VP team (speech/language pathologist, pediatric otolaryngologist and plastic surgeon) to determine the extent and the pattern of VP closure. The results were analyzed using Wilcoxon-Rank and Kruskal-Wallis statistical tests with significance assigned at p<0.05. Results: Of the 155 patients analyzed, 122 (77%) had overt or submucous cleft palate while 36 (23%) had VPD without cleft. The presurgical VP closure pattern, as seen on VNE, was distributed into three groups: coronal (38%), circular (19%), and hypodynamic/adynamic (34%). Hypodynamic/adynamic was defined as closure of less than 50% of resting VP port area. Frequency of distribution within these closure patterns did not significantly differ between cleft and non-cleft VPD patients. All symptoms of VPD (HN, NE and NT) improved significantly following SP. The greatest improvement in perceptual score occurred with HN with mean improvement of 2.4 ranks (p<0.0001). Nasal emissions improved by a mean of 1.1 ranks (p<0.001), and NT improved by a mean of 0.4 ranks (p=0.015). Improvement in perceptual ratings was not significantly associated with presence of cleft. Presence of an associated syndrome, e.g. velocardiofacial syndrome (q22 chromosomal deletion) had no significant effect on the postoperative VP outcome. Analysis of the link between the presurgical VP closure pattern and the VP functional outcome demonstrated that patients with hypodynamic /adynamic closure pattern showed the greatest improvement in HN; improvement in HN for coronal and circular patterns was also statistically significant (p=0.022). Conclusions: Sphincter pharyngoplasty is a very effective means of improving hypernasality, and to a lesser degree nasal emission and nasal turbulence, in individuals with velopharyngeal dysfunction. The efficacy of sphincter pharyngoplasty is independent of both the presence or absence of a cleft palate and the presence or absence of an associated syndrome. Contrary to some expectations, sphincter pharyngoplasty is most beneficial for patients with a hypodynamic or adynamic velopharynx.