Objectives: To examine disease, treatment, cognitive, and psychological factors associated with quality of life (QoL) before and after surgery and assess the ability to predict QoL outcomes. Methods: We identified a retrospective, cross-sectional sample of 85 patients with Parkinson disease who underwent subthalamic deep brain stimulation (DBS). Patients' QoL was categorized as "improved" and "stable/worsened" using reliable change indices. Univariate correlational analyses identified relationships between Parkinson's Disease Questionnaire-39 ratings and disease (Unified Parkinson's Disease Rating Scale-III [UPDRS-III] motor scores on and off medications, disease duration), treatment (medication burden, unilateral vs bilateral DBS), cognitive (neuropsychological battery), and psychological (depression) variables. Step-wise multiple linear regression and logistic regression models included selected preoperative variables to predict change in QoL ratings and QoL outcome after surgery. Results: Fifty-one percent of patients reported clinically significant improvements in QoL while 47% reported stable QoL and 2% worsened. Motor scores (UPDRS-III) were not relevant to QoL changes, potentially because of the rarity of poor motor outcomes, while single-trial learning and depression scores were the most important variables in predicting QoL changes. There was a subtle additional benefit to undergoing bilateral subthalamic nucleus DBS. Conclusions: The findings provide greater insight into the nonmotor features that contribute to the success of subthalamic nucleus DBS procedures from the patient's perspective and raise questions about the treatment focus and emphasis on symptom profiles in DBS candidacy evaluations.