Context This study was part of a large double-blind sham surgery–controlled trial designed to determine the effectiveness of transplantation of human embryonic dopamine neurons into the brains of persons with advanced Parkinson's disease. This portion of the study investigated the quality of life (QOL) of participants during the 1 year of double-blind follow-up.

Objectives To determine whether QOL improved more in the transplant group than in the sham surgery group and to investigate outcomes at 1 year based on perceived treatment (the type of surgery patients thought they received).

Design Participants were randomly assigned to receive either the transplant or sham surgery. Reported results are from the 1-year double-blind period.

Setting Participants were recruited from across the United States and Canada. Assessment and surgery were conducted at 2 separate university medical centers.

Participants A volunteer sample of 40 persons with idiopathic Parkinson's disease participated in the transplant ("parent") study, and 30 agreed to participate in the related QOL study: 12 received the transplant and 18 received sham surgery.

Interventions Interventions in the parent study were transplantation and sham brain surgery. Assessments of QOL were made at baseline and 4, 8, and 12 months after surgery.

Main Outcome Measures Comparison of the actual transplant and sham surgery groups and the perceived treatment groups on QOL and medical outcomes. We also investigated change over time.

Results There were 2 differences or changes over time in the transplant and sham surgery groups. Based on perceived treatment, or treatment patients thought they received, there were numerous differences and changes over time. In all cases, those who thought they received the transplant reported better scores. Blind ratings by medical staff showed similar results.

Conclusions The placebo effect was very strong in this study, demonstrating the value of placebo-controlled surgical trials.