The results indicate that although in the female transsexuals the values of the acoustic parameters decreased; there was only immediate effect in Local Jitter, Jitter APQ5, Harmonic-noise ratio and Fundamental frequency (F0); that shows that the female's voice became high-pitched. In male transsexuals, F0 was modified after therapy, then the voice became more deep. It is concluded that TVSO therapy has an immediate effect mainly on Jitter and F0 and can be considered an alternative, viable and complementary therapy in the process of masculinization and feminization of voice.