This study investigated the role of loudness perception and selected auditory processes in 17 participants with hypophonia related to Parkinson's disease (PD) and 25 controls. For most of the five loudness perception tasks (magnitude estimation, imitation, speech-to-noise judgment, magnitude production, magnitude production in noise), the PD participants produced a significantly different pattern and used a more restricted range than the controls in their self-generated estimates of speech intensity and judgments of speech loudness.Results from two self-assessment questionnaires (CETI-M, M-SAPP) found that the PD participants perceived themselves as less effective communicators than controls. An audiometric evaluation suggested that the PD participants may have abnormalities related to higher admittance values, higher acoustic reflex thresholds and higher pure-tone thresholds for lower frequencies. These results suggest that individuals with PD may have a speech loudness perception deficit involving the abnormal perception of externally-generated and self-generated speech intensity stimuli.