The aim of this study was to determine the importance of the closed quotient in the improvement of voice quality after medialization thyroplasty by measuring acoustic parameters at the sentence level. The clinical records of patients who received type I thyroplasty were reviewed retrospectively. All of the patients underwent the perceptual, acoustic, and aerodynamic evaluation before the surgery and on the 60th postoperative day. The perceptual and acoustic measurements were obtained from a recording of a passage read aloud by the patients. Acoustic and aerodynamic parameters were investigated. A paired t test was used to compare presurgery and postoperative results. A correlation analysis was also used to discern which parameters were most correlated with improvement of postoperative voice quality. Statistically significant improvements were observed in subglottic pressure (Psub), maximum phonation time, and mean flow rate. Average fundamental frequency and average closed quotients were found to be the parameters that were most associated with an improvement of postoperative breathiness. The /G/ grade of GRBAS scale quality was found to be most associated with Psub and shimmer (P<0.05). An increase of the contact area of both vocal folds induced improvement in aerodynamic parameters and led to the stabilization of vocal fold vibration. This effect resulted in improvement of the acoustic parameters (shimmer, jitter, signal-to-noise ratio, voice range profile) and voice quality.