OBJECTIVE/HYPOTHESIS To determine whether knowledge of medical diagnosis biases listeners with varied experience levels in their judgments of dysphonia. STUDY DESIGN Prospective, mixed experimental and comparative design. METHODS Twenty-six speakers with dysphonia and four normal controls provided speech recordings. Twenty novice and eight experienced clinicians evaluated speech samples for roughness and breathiness using 100-mm visual analog scales. In one condition, the speech samples were presented without diagnostic information; in the second condition, samples were presented in conjunction with the medical diagnosis. RESULTS Regardless of experience level, listeners judged the samples as significantly more severe when the speakers' diagnoses were known. Specifically, novice listeners (NLs) significantly increased the severity of judgments for speakers who were mildly breathy or mildly or moderately rough when diagnostic information was known. In addition, listeners in both groups judged speakers with mass lesions to be significantly rougher when diagnosis was known; this bias was not observed for speakers with other diagnoses. NLs also trended toward increasing the severity of breathiness judgments for individuals with known vocal fold paralysis but not other diagnoses. CONCLUSIONS Sources of bias such as knowledge of medical diagnoses should be considered when listeners with varied experience levels use auditory-perceptual measures to evaluate dysphonia.