OBJECTIVES: To assess whether combined surgery and best medical therapy resulted in better outcomes than best medical therapy alone, in patients with advanced Parkinson’s disease (PD). METHODS: The PD SURG trial is an ongoing randomised, open-label trial. At 13 neurosurgical centres in the UK, between November 2000, and December 2006, patients with PD (that was not adequately controlled by medical therapy) were assigned to either, combined surgery and best medical therapy, or to best medical therapy alone. The primary endpoint was the quality of life PRO measure, the 39-item Parkinson’s disease questionnaire (PDQ-39). Changes between baseline and 1 year were compared by use of t tests. RESULTS: 366 patients were randomly assigned to receive immediate surgery and best medical therapy (183) or best medical therapy alone (183). All patients who had surgery had deep brain stimulation. At 1 year, the mean improvement in PDQ-39 summary index score compared with baseline was 5.0 points in the surgery group and 0·3 points in the medical therapy group (difference –4·7, 95% CI –7·6 to –1·8; p=0.001); the difference in mean change in PDQ-39 score in the mobility domain between the surgery group and the best medical therapy group was –8·9 (95% CI –13·8 to –4·0; p=0.0004), in the activities of daily living domain was –12·4 (–17·3 to –7·5; p<0.0001), and in the bodily discomfort domain was –7·5 (–12·6 to –2·4; p=0.004). Differences between groups in all other domains of the PDQ-39 were not significant. Other serious adverse events will be reported. CONCLUSIONS: At one year, surgery and best medical therapy improved patient self-reported quality of life more than best medical therapy alone in patients with advanced Parkinson’s disease. These differences are clinically meaningful, but surgery is not without risk and targeting of patients most likely to benefit might be warranted.