Objective: To review the safety of simultaneous bilateral posterior cricoarytenoid muscle botulinum toxin injections. Design: Retrospective case series review. Setting: Tertiary care academic clinic. Patients: Twenty-one patients with abductor spasmodic dysphonia. Interventions: Patients received 100 simultaneous bilateral posterior cricoarytenoid muscle botulinum toxin injections for isolated abductor spasmodic dysphonia over a 6-year period. Main Outcome Measures: Major and minor complications, injection dosing, and demographics. Results: The total bilateral botulinum toxin injection dose per session ranged from 2.50 to 7.50 U, and the average total bilateral dose per patient was 4.70 U. There were no major complications, and minor complications were self-limited. There was a 5% incidence of significant dyspnea and a 2% incidence of dysphagia, and all patients were treated conservatively. The average doses at which dyspnea and dysphagia occurred were 4.97 and 5.56 U, respectively. Conclusions: This case series demonstrates that simultaneous bilateral posterior cricoarytenoid muscle botulinum toxin injection is safe up to the highest doses reported. Complications with this approach are consistent with those previously reported using other methods. Prospective studies on vocal outcome measures are needed for simultaneous bilateral posterior cricoarytenoid muscle botulinum toxin injections to evaluate the efficacy of this technique. ©2005 American Medical Association. All rights reserved.