Objectives. To study the effects of biofeedback on voice sound level (SL) in subjects with reduced voice SL, secondary to Parkinson disease (PD), using a portable voice accumulator. Study Design: Prospective intervention study. Methods: Voice SL, phonation time, and level of background noise were registered with a portable voice accumulator during three consecutive registration periods. Six subjects with reduced voice SL secondary to PD participated. Biofeedback, in the form of a vibration signal when voice SL went below an individually set threshold level, was administered during the second registration period only. Mean voice SL was calculated for registration periods with and without feedback. Data on phonation time and level of background noise was also collected. Field registrations with the portable voice accumulator were also compared with registrations made in a recording studio. In addition, subjects were asked about subjective experiences of using the portable voice accumulator for up to 15 days. Results: There was a statistically significant increase in voice SL during the period when biofeedback of voice SL was administered. Subjects reported that using the portable voice accumulator was a positive experience. Several participants wished to continue using the device. In general, subjects handled the device independently with no major problems and did not report any negative experiences. Conclusions: Although this study was a first trial including six subjects with reduced voice SL secondary to PD, the findings indicate that biofeedback of voice SL administered via a portable voice accumulator may be a useful treatment tool for this group of patients and that further studies are needed.