Deep brain stimulation of the subthalamic nucleus (STN-DBS) improves the motor difficulties experienced by patients with Parkinson's disease (PD); however, the effects on speech are variable. In this study, patients rated their current post-surgery speech difficulties using the Voice Handicap Index (VHI) and used the same measure to retrospectively rate their pre-surgery speech. Scores pre- and post-surgery were also available on the UPDRS-III, and the patients' intelligibility was assessed by an independent listener. A control group of non-surgical patients with PD (medical group) also completed the VHI for comparison. VHI scores deteriorated equally in the two groups. However, the variability of the change scores in the surgical group was significantly greater than in the medical group. The correlation between the changes in the VHI and UPDRS scores for the surgical group was not significant. Correlations between the VHI scores and intelligibility were significant both before and after surgery, suggesting that patients accurately perceive their difficulties. The findings confirm the variability in the speech difficulties of patients following STN-DBS. The patients' ability to use the VHI offers a means of assessing the effects of their speech on their quality-of-life, and may be clinically useful post-STN-DBS.