Psychological stress can influence vocal quality. The purpose of the present study was to determine the effect of stress on female vocal quality. In this experimental study 54 female voices were studied in a stress-inducing and a relaxed condition. In the stress-inducing condition the subjects were asked to read a passage while instructions were used to evoke stress. In the relaxed condition the same reading task but without specific instructions was used. Identical subjective and objective assessment techniques were used to determine vocal quality in the stressed and the relaxed conditions. In stress-inducing and challenging conditions the female voice is more breathy, strained and of a lower objective vocal quality characterized by lower fundamental frequency, lower frequency, intensity and aerodynamic capacity. This study indicates that stress-inducing and challenging conditions change vocal quality and vocal performance. Understanding of the effect of stress on voice production is relevant for clinical diagnostic situations, particularly in patients who present with a functional (nonorganic) voice disorder, as well as those patients who have some organic pathology but who also report exacerbation of symptoms during periods of increased life stress.