This article reports a pilot study of the effect of tai chi (TC), a pharmacological adjunct and mild aerobic exercise, on osteoarthritic knee pain in elders with cognitive impairment (CI). The TC program included a warm-up, 12-form Sun-style TC, and a cool-down period, for a total of 20-40 minutes per session, twice a week for 15 weeks. The results showed no significant differences in knee pain after the TC intervention in 7 elders with CI. However, more minutes of TC attendance were related to improved pain scores (Spearman's rho = .78, P <.05). Greater accuracy in TC performance was also correlated with improvements in pain scores (Spearman's rho = .70, P = .08). Of 4 elders who participated in TC practice regularly (more than 20 sessions), 3 showed clinically important improvements, but 3 elders who participated in no sessions or only a few sessions showed no improvement.