Parkinson's disease (PD) is the second most common neurodegenerative disease (Twelves D, Perkins KS, Counsell C. Mov Disord 18:19-31, 2003) and afflicts more than four million people worldwide (Dorsey ER, Constantinescu R, Thompson JP, et al. Neurology 68:384-386, 2007). Neurosurgical treatments for the debilitating symptoms of this movement disorder are implemented when medical therapy no longer provides sufficient benefit. Lesioning techniques initially utilized decades ago have been supplanted, for the most part, by deep brain stimulation (DBS) because of its potential reversibility should DBS prove to be unsuccessful or result in undue adverse events. Additionally, stimulation parameters can be adjusted as needed to optimize benefit (from both motor and neurobehavioral standpoints), and when bilateral procedures are necessary, DBS procedures are considered a safer alternative or adjunct to ablation. Stimulation of the subthalamic nucleus (STN) is currently the target of choice because it relieves most of the cardinal symptoms of PD and greatly reduces the amount of medication needed. Evaluation of postsurgical behavioral changes is complex because there is no universal methodology that allows direct comparisons among studies, which not only results in disparate findings across studies but precludes generalizability. Nevertheless, it is necessary to document change, be it beneficial or detrimental, in order to guide informed decision making regarding future treatment and/or rehabilitation. Although modern-day techniques are often deemed "relatively safe" from a cognitive and behavioral standpoint, there is mounting evidence that cognitive and psychiatric morbidities do occur quite frequently. Decline in verbal fluency is the most common finding, regardless of ablation or DBS techniques, but studies provide evidence of wide-ranging deficits in other aspects of cognition as well, albeit often not clinically significant for the patient. In contrast, psychiatric and mood disturbances observed with alarming frequency especially after STN-DBS, significantly compromise patients' daily functioning and quality of life (QOL), and may even lead to death. So the question remains as to whether we can really say with certainty that surgical treatment is "safe." Optimal cognitive and behavioral outcomes depend on appropriate selection of surgical candidates informed by detailed pre- and postoperative assessment of cognitive and psychiatric status.