Background: Speaking louder/more intensely represents a longstanding technique employed to manage voice and intelligibility changes in people with Parkinson's. This technique has been formalized into a treatment approach and marketed as the Lee Silverman Voice Treatment (LSVT®) programme. Evidence for its efficacy has been published. Studies to date are dominated by research facility reports from the original LSVT® group or closely associated groups. Evidence for the efficacy of LSVT® in routine clinical settings is lacking. Methods & Procedures: We conducted an audit of outcomes for consecutive people with Parkinson's who were offered and completed LSVT® in a routine hospital outpatient setting. In- and exclusion criteria, assessment and treatment protocols followed precisely the methods stipulated by LSVT® Global. Additionally, participants completed the Voice Handicap Index (VHI) and 23 carers completed a visual analogue scale (VAS) for items relating to functional outcomes. Outcomes & Results: Group data (n = 33) revealed statistically significant increases in all objective and subjective measures at the end of treatment, though outcomes on the different measures revealed variable individual responses. Mean intensity increases on prolonged vowel were 9.3 dB post-treatment. Significant gains of mean 7.5 and 6.8 dB were maintained at 12 (n = 25) and 24 months (n = 15) respectively for those available for follow-up. Significant intensity gains occurred for reading post-therapy (mean = 8.5 dB), but changes reverted to statistically non-significant at 12 and 24 months. Intensity increase (mean = 8.5 dB) was significant for monologues post-therapy, but not at 12 and 24 months. Median VHI improvement was statistically significant post-therapy and at 12 months, but not at 24 months. Carer VAS ratings all improved significantly post-therapy; at 12 months only perceived loudness, strain, mumbling and intelligibility remained statistically significantly above baseline. No significant gains persisted to 24 months. Conclusions & Implications: LSVT® was successful for most individuals in this study. Not all patients attained significant changes by the end of treatment. Few patients who achieved significant gain at the end of treatment maintained this at 12 or 24 months. Implications for maintenance, interpretation of results in a degenerative condition and implications for further research are discussed.