Object. Postoperative psychiatric symptoms have been associated with subthalamic deep brain stimulation (DBS) for Parkinson disease (PD), and preoperative psychiatric vulnerability, the effects of surgery, stimulation, medication changes, and psychosocial adjustment have been proposed as causative factors. The variables involved in whether preoperative psychiatric symptoms improve or worsen following surgery are not yet known. In the present study, preoperative psychiatric symptoms were systematically assessed in patients with PD presenting for routine preoperative psychiatric assessment. Methods. Forty consecutive patients with PD presenting for DBS were interviewed using the Mini International Neuropsychiatric Inventory. Current depressive symptoms were quantified using clinician- and patient-rated depression scales. Seventy-eight percent of patients had at least one lifetime or current Axis I psychiatric diagnosis. The prevalence of depression was 60% (95% confidence interval [CI] 45–85), psychosis 35% (95% CI 25–50), and anxiety 40% (95% CI 25–55). These prevalence rates were comparable to or greater than those in the general population of patients with PD. Twenty-three percent of patients required psychiatric treatment for current symptoms prior to being considered eligible for DBS. Conclusions. As part of the selection process for surgery, members of the study population were chosen for their lack of overt dementia or other active disabling psychiatric symptomatology. The incidence rates of psychiatric disorders, including those diseases occurring in the general population affected with PD, were greater than expected. Data in the present study lead one to question the reliability of patient-rated depression scales as the sole instrument for assessing depression. The authors highlight the need for evidence-based guidelines in the management of these preoperative symptoms as well as the involvement of psychiatric personnel in the assessment and management of these symptoms.