Recently, with the evolution of surgical procedures for the improvement of voice, various studies on diagnostic method of accurate laryngeal function of patients of the voice disorders by various laryngeal diseases has been carried on. The evaluation methods of laryngeal function which had been used in the previous studies can be classified as follows ; Aerodynamic test which is valuable for evaluation of phonatory function, vibration test of vocal cord by laryngostroboscopy and ultra high speed motion picture which is to investigate vocal cord vibration in detail, acoustic evaluation by sound spectrography which gives visual presentation of the three parameters of the acoustical structure of voice-frequency, intensity, time and psychoacoustic evaluation of voice by standarized parameters which have been made by and otolaryngologist. Hence, in order to identify the phoniatrical characteristics of various laryngeal diseases (vocal cord paralysis, laryngeal polyp, vocal nodule, laryngeal papilloma, sulcus vocalis, Reinke's edema, laryngeal carcinoma, laryngitis, spastic dysphonia) and to shed some light on prevention, diagnosis, and treatment, the authors practiced the tests mentioned above. 345 patients who had been visited to Vocal Dynamics Laboratory of this hospital from May, 1981 until August, 1982 were observed through the tests : The followings are the findings of the study. 1) Most of the disorders showed the highest incidence between twenties and forties. The laryngeal disorders in order of frequency were 25% in vocal nodule, 17% in laryngeal polyp, 16% in laryngitis, 15% in vocal cord paralysis, 13% in sulcus vocalis which were above 80% of various laryngeal disorders. 2) The results of the aerodynamic test are : a. Generally maximum phonation time was below the normal level in vocal cord paralysis, bilateral laryngeal polyp, vocal nodule, and laryngeal papilloma, while in other diseases, it was the normal level. b. Phonation quotients and mean flow rates were above the normal level in most of the voice disorders but spastic dysphonia was the normal level. 3) The results of the laryngostroboscopy are : a. Symmetricity was not shown consistently in most of the voice disorders but unilateral Reinke's edema, vocal nodule and spastic dysphonia showed symmetricity and unilateral vocal cord paralysis, laryngeal papilloma and laryngeal carcinoma showed asymmetricity in general. b. Regularity of vibration was regular in most of the voice disorders but unilateral vocal cord paralysis and bilateral laryngeal polyp only showed irregularity. c. Glottic closure was not complete in most of the voice disorders but spastic dysphonia showed completeness. d. Amplitude was not shown in most of the voice disorders consistently but vocal cord paralysis, laryngeal polyp, laryngeal papilloma and laryngeal carcinoma were small and absent mostly. e. Mucosal wave was not shown consistently in most of the voice disorders but, in general, laryngeal carcinoma, bilateral sulcus vocalis, and laryngeal papilloma were small or absent and Reinke's edema was great. f. Non-vibrating portion was shown in vocal cord paralysis, laryngeal polyp, laryngeal papilloma, and laryngeal carcinoma but it was absent in sulcus vocalis, Reinke's edema, and spastic dysphonia. 4) The results of psychoacoustic evaluation are : a. Most of the voice disorders showed the hoarseness but there are many cases of vocal nodule and laryngitis which showed no hoarseness, and bilateral laryngeal papilloma and spastic dysphonia showed severe hoarseness. b. When we looked into the characteristics of the hoarseness of the various voice disorders, we found generally that asthenic and breathy in vocal cord paralysis, asthenic in sulcus vocalis, rough in laryngeal polyp, vocal nodule, Reinke's edema, laryngitis and laryngeal carcinoma, strained in spastic dysphonia were noted.