We found that a program of twice-weekly tai chi for 24 weeks, as compared with a resistance-training program or a stretching program, was effective in improving postural stability and other functional outcomes in patients with mild-to-moderate Parkinson’s disease. Tai chi training also significantly reduced the incidence of falls, as compared with the stretching program. Improvements in primary and secondary outcomes were maintained 3 months after the intervention, a finding that is consistent with prior research involving adults 70 years of age or older.13 No serious adverse events were observed during tai chi training, indicating the safety and usefulness of this intervention for persons with Parkinson’s disease.