Cases diagnosed as essential voice tremor were studied by (1) clinical statistics and (2) acoustic analytical assessments. (1) Patients with this disorder accounted for 0.06 % of the overall new outpatient population. Among 20 patients with essential voice tremor studied, there were more women than men, and patients with onset of the illness in their sixties were most frequent. (2) Sound spectrographic samples of the five vowels were analyzed with respect to frequency of voice tremor, fluctuation of fundamental frequency, PPQ, APQ, Jitter % and Shimmer %. Analysis revealed significant differences in frequency of voice tremor and APQ between /a/ and /u/, thus indicating that vocal symptoms vary for each vowel. To explore the effect of acoustic impedance on these acoustic parameters, experiments were performed using three types of cylinders differing in shape of the aperture. The results of the experiment showed that the frequency of voice tremor is lower at a larger acoustic impedance. The findings also demonstrated that acoustic factors have a bearing on the characteristics of essential voice tremor.