Introduction: The botulinum toxin injection guided by eletromiography into the thyroarytenoid muscle has been the most accepted treatment for adductor spasmodic dysphonia. This method, however, requires the eletromiography equipment and a trained team for its use, which may not be available in some institutions. Aim: The aim of this work is to make a detailed description of the injection through the nasolaryngoscope, pointing out important factors related to the success and also to some failures. Material and method: In face of those difficulties, we introduced the technique for injection of botulinum toxin through the flexible nasolaryngoscope. Conclusion: This is the most used technique at the Clinics Hospital of São Paulo University Medical School since 1994 and has shown to be very efficient and easy to be handled.