This pilot study examines the effects of Tai Chi on balance, gait and mobility in people with Parkinson disease (PD). Thirty-three people with PD were randomly assigned to either a Tai Chi group or a control group. The Tai Chi group participated in 20 one-hour long training sessions completed within 10–13 weeks; whereas, the control group had two testing sessions between 10 and 13 weeks apart without interposed training. The Tai Chi group improved more than the control group on the Berg Balance Scale, UPDRS, Timed Up and Go, tandem stance test, 6-minute walk, and backward walking. Neither group improved in forward walking or the one leg stance test. All Tai Chi participants reported satisfaction with the program and improvements in well-being. Tai Chi appears to be an appropriate, safe and effective form of exercise for some individuals with mild-moderately severe PD.