OBJECTIVE: Evaluate vocal quality in patients with OSA before and after continuous use of CPAP with a humidifier using subjective patient perception and clinical assessment. The hypothesis was that CPAP treatment with a humidifier would benefit voice quality. STUDY DESIGN: Randomized, sham-controlled, blinded clinical trial. METHODS: Forty-three natal males with obstructive sleep apnea for whom CPAP treatment was recommended following polysomnography were randomized into two therapy groups: CPAP and Sham-CPAP. Participants completed questionnaires on voice use, a voice self-assessment with the ten-item vocal handicap index (VHI-10), and complementary questionnaires: the Epworth sleepiness scale (ESS), Pittsburgh sleep quality index (PSQI), reflux symptoms index (LPRSI) and oral dryness visual analog scale (DRY). Their voices were recorded at three different times: before CPAP therapy, and after 3 and 6 months of continuous CPAP use. The acoustic voice quality index (AVQI), and an auditory-perceptual judgment (APJ) were also applied before and after the CPAP and Sham treatments. RESULTS: After 6 months of treatment, the CPAP group presented improvements in their sleep patterns; however, no statistically significant differences were observed between the groups in respect of the results of the voice-related questionnaires, the AVQI values, and the APJ of the voice quality. All of the participants had some degree of vocal deviation at baseline. CONCLUSIONS: CPAP therapy with a humidifier did not improve vocal quality as evaluated by the clinician or patient self-assessment. However, it did not have any significant negative effects on voice quality, so can be considered safe to use in male OSA patients.