Patients practicing Tai Chi will exhibit significant improvements in primary outcome measures of balance, and secondary outcomes of gait, physical performance, Unified Parkinson's Disease Rating Scale, Falls, muscle strength.

The study is designed to determine the effects of Tai Chi training on balance and other functional outcomes in persons with Parkinson's disease.

Inclusion Criteria:

Patients who have:

• A diagnosis of idiopathic PD, with a disease severity rating of stage I to IV on the Hoehn and Yahr scale (Hoehn & Yahr, 1967)
• At least 1 score of 2 or more for at least 1 limb for either the tremor, rigidity, or bradykinesia item of the Unified Parkinson's Disease Rating Scale (UPDRS)
• Stable medication usage
• Not participated in a structured exercise program (i.e., not involved in any routine, organized physical activity program lasting 30 minutes or more per day, such as a gym program or regularly scheduled instructor-led exercise class) in the previous 2 months
• Ability to stand unaided or walk independently; had a personal physician's or neurologist's clearance for participation; and had a willingness to be assigned to intervention conditions.

Exclusion Criteria:

Patients who:

• Participate in any other behavioral or pharmacological research study
• Have cognitive decline (Mini-Mental State Examination score, ≤ 24) (Folstein et al., 1975)
• Have self-reported diagnosis of Alzheimer disease or other severe neurological (stage III and IV PD)
• Have evidence of progressive or debilitating conditions (metastatic cancer, severe heart or lung disease, crippling arthritis) or severe losses in vision and hearing that would limit their tolerance to testing and training procedures, that would interfere with study participation
• Are unavailable during the study period.