Deficits in balance and gait may lead to falls, fall-related complications, and physical inactivity in people with PD. These negative effects are thought to lead to a 'malignant' form of PD in which there is reduced quality of life and increased risk for mortality. While people who have had STN-DBS often experience reductions in tremor, rigidity, and bradykinesia, surgical management of PD may not be effective in ameliorating impairments in balance and gait. In fact, investigators have reported that DBS may worsen balance, which may accelerate an individual's decline toward 'malignant' PD. To this end, recent studies indicate physical activity levels did not increase after STN-DBS. This finding should not go unnoticed as physical activity may have a disease modifying effect, slowing the progression of motor disability. As of 2011, approximately 70,000 people with PD have undergone DBS, with the annual number of DBS procedures for PD totaling between 8,000-10,000. In addition, investigators are now studying the effects of STN-DBS in people with early PD. The procedure appears to be safe and effective in this population, which will increase the number of surgical candidates. With the number of people with PD expected to double to more than 8 million by 2030, the number of those receiving DBS is expected to substantially increase.