Adductor Spasmodic Dysphonia (ASD) is a neurological disorder of central motor processing, characterized by involuntary and inappropriate contractions of the phonatory muscles, producing hyperadduction of the vocal folds, which causes a tremulous, faltering and strained-strangled voice. The aim of this study was to describe the vocal, acoustic and laryngeal parameters measured for a female patient with ADS pre and post speech therapy using the Technique of Sustained Maximum Phonation Time (SMPT). This technique aims to promote increase in glottal resistance, improve phonatory stability, and enhance glottal coaptation. A 66-year-old female patient with ASD took part in this study. She was submitted to otorhinolaryngologic and speech-language assessment before and after the application of the SMPT technique. The results showed modification of vocal, acoustic and laryngeal parameters, such as re-classifying her dysphonia from G3R1B1A0S3I3 to G2R1B1A0S2I2, her pitch from severe to adequate, her spectrographic trace from unstable to more stable, and an expressive increase in mean fundamental frequency and mean vocal intensity, besides improvement of her glottal efficiency, with closure of the anteroposterior glottal opening. Speech therapy using the SMPT technique was considered a suitable treatment option for this case, given the good results obtained, especially the improvements in vocal quality and phonatory stability. The importance of further studies with the aim to provide greater scientific evidence for the effectiveness of the technique when treating ASD is emphasized.