SUMMARY: The aim of this study was to investigate the acoustic and electroglottographic characteristics of patients with mutational dysphonia before and after voice therapy. The clinical records of 15 patients with mutational dysphonia were reviewed, and their voice recordings were analyzed with the help of the Lx Speech Studio program (Laryngograph Ltd, London, UK). After voice therapy combined with the manual compression method, the subjects' voices lowered in pitch and improved in quality. In addition, we classified the mutational dysphonia into four categories according to the presence of diplophonia and closed quotients. The most common type among the categories was characterized by a bimodal distribution of fundamental frequency (diplophonia), accompanied by a low closed quotient (falsetto voice) at high frequencies. However, the results also showed that mutational dysphonia cannot be generalized as always having a falsetto voice, as shown in other types. The effect of therapy was different for each type, and those cases with both diplophonia and a non-trained falsetto voice could be treated more readily. Consequently, the diplophonia and closed quotient, which were easily analyzed using Lx Speech Studio program, are important factors in the classification of mutational dysphonia. Identification of these characteristics may affect treatment choices, facilitate monitoring of the efficacy of therapy, and aid in estimating prognosis.