Objectives: Augmentation of vocal fold with hyaluronic acid (Restylane; Q-Med AB, Uppsala, Sweden) is used as a therapeutic option for insufficient glottic closure in unilateral vocal fold paralysis (UVP). Analysis of the optimal glottic width, effectiveness (long-term voice improvement as a consequence of longevity of Restylane), and safety of this new method was made. Study Design/Methods: In a prospective clinical cohort study, 19 consecutive patients with UVP who received vocal fold augmentation with hyaluronic acid (Restylane) were examined preoperatively; 6 weeks, 6, and 12 months postoperatively by laryngostroboscopy; and their voice was evaluated by subjective, objective, and self-assessment (Voice Handicap Index). Results: In 11 of 19 (58%) patients, a subjectively and objectively acceptable voice quality was observed in a follow-up of 12 months. Eight of 19 (42%) patients had a considerable impairment of the voice after 6 weeks (range: 1-24 weeks). Therefore, another intervention (eg, injection laryngoplasty or thyroplasty) was recommended. An impairment of voice was mainly observed if the preoperative glottal gap during phonation was more than 1 mm. Conclusion: A long duration (up to 12 months) of acceptable quality of voice was achieved by augmentation with Restylane, if the glottal gap was 1 mm or less videolaryngostroboscopically during phonation. The authors recommend this therapy for temporary voice improvement and to augment vocal therapy, if spontaneous recovery of voice is likely. Long-term results remain to be seen.