The purpose of this study is to clarify the mechanism of the adduction of ventricular folds during phonation. We assessed the type and degree of adduction of ventricular folds during phonation by fiber-stroboscopy in 277 cases of unilateral laryngeal nerve paralysis. In 169 cases of the 277 assessed, adduction of the ventricular folds occurred during phonation (61%), which was produced by the unaffected ventricular fold. Five cases (2%) exhibited adduction of the affected ventricular fold. There was no sex difference observed in the cases in which adduction of ventricular folds occured during phonation. As compared to nonadduction, the incidence of marked hyperadduction significantly increased with age in the later part of life. As for the maximum phonation time (MPT), the mean flow rate (MFR), and the SPL-range during the vocal function test, cases of marked hyperadduction of the ventricular folds showed significant reduction as compared with these with nonadduction. Regarding the pitch perturbation quotient (PPQ), the amplitude perturbation quotient (APQ) and the normalized noise energy (NNE) determined during the acoustic analysis, cases of marked hyperadduction of the ventricular folds showed significant reduction as compared with those of nonadduction. In many cases, reduction of the affected vocal fold function was observed in cases in which the fixed position of the vocal fold on the affected side was intermediate. In other words, the adduction of the ventricular folds was regarded as a compensatory reaction to glottal insufficiency. In 206 cases in which a silicon injection was performed, we compared the degree of adduction of the ventricular fold before and after the silicon injection. It is notable that following a silicon injection the degree of adduction was reduced in 106 (84%) out of the 126 cases in which adduction of ventricular folds was observed prior to injection.国立情報学研究所で電子