Spasmodic dysphonia (SD) is a rare voice disorder, which severely affects the vocal mechanism. Early and accurate diagnosis is important in planning suitable treatment strategy. The purpose of this study was to describe the major clinical characteristics of SD which are the keys to diagnosis. The subjects included 30 patients diagnosed as having SD at the National Ear Nose Throat Hospital. The patients underwent interviews for subjective symptoms, perceptual voice analysis, acoustic analysis, and video strobolaryngoscopy. The authors found that most of the patients had strangled, strain voice quality and voice breaks. Acoustic analysis of the voices showed phonatory breaks, frequency shifts, signal aperiodicity, and amplitude modulation. Video strobolaryngoscopy showed decreased and chaotic mucosal wave, and strong glottal and supraglottal constrictions.