© 2019 The Cochrane Collaboration. Background Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory, autoimmune disease that results in joint deformity and immobility of the musculoskeletal system. The major goals of treatment are to relieve pain, reduce inflammation, slow down or stop joint damage, prevent disability, and preserve or improve the person’s sense of well-being and ability to function. Tai Chi, interchangeably known as Tai Chi Chuan, is an ancient Chinese health-promoting martial art form that has been recognized in China as an effective arthritis therapy for centuries. This is an update of a review published in 2004. Objectives To assess the benefits and harms of Tai Chi as a treatment for people with rheumatoid arthritis (RA). Search methods We updated the search of CENTRAL, MEDLINE, Embase, and clinical trial registries from 2002 to September 2018. Selection criteria We selected randomized controlled trials and controlled clinical trials examining the benefits (ACR improvement criteria or pain, disease progression, function, and radiographic progression), and harms (adverse events and withdrawals) of exercise programs with Tai Chi instruction or incorporating principles of Tai Chi philosophy. We included studies of any duration that included control groups who received either no therapy or alternate therapy. Data collection and analysis We used standard methodological procedures expected by Cochrane. Main results Adding three studies (156 additional participants) to the original review, this update contains a total of seven trials with 345 participants. Participants were mostly women with RA, ranging in age from 16 to 80 years, who were treated in outpatient settings in China, South Korea, and the USA. The majority of the trials were at high risk of bias for performance and detection bias, due to the lack of blinding of participants or assessors. Almost 75% of the studies did not report random sequence generation, and we judged the risk of bias as unclear for allocation concealment in the majority of studies. The duration of the Tai Chi programs ranged from 8 to 12 weeks. It is uncertain whether Tai Chi-based exercise programs provide a clinically important improvement in pain among Tai Chi participants compared to no therapy or alternate therapy. The change in mean pain in control groups, measured on visual analog scale (VAS 0 to 10 score, reduced score means less pain) ranged from a decrease of 0.51 to an increase of 1.6 at 12 weeks; in the Tai Chi groups, pain was reduced by a mean difference (MD) of-2.15 (95% confidence interval (CI)-3.19 to-1.11); 22% absolute improvement (95% CI, 11% to 32% improvement); 2 studies, 81 participants; very low-quality evidence, downgraded for imprecision, blinding and attrition bias. There was very low-quality evidence, downgraded for, blinding, and attrition, that was inconclusive for an important difference in disease activity, measured using Disease Activity Scale (DAS-28-ESR) scores (0 to 10 scale, lower score means less disease activity), with no change in the control group and 0.40 reduction (95% CI-1.10 to 0.30) with Tai Chi; 4% absolute improvement (95% CI 11% improvement to 3% worsening); 1 study, 43 participants. For the assessment of function, the change in mean Health Assessment Questionnaire (HAQ; 0 to 3 scale, lower score means better function) ranged from 0 to 0.1 in the control group, and reduced by MD 0.33 in the Tai Chi group (95% CI-0.79 to 0.12); 11% absolute improvement (95% CI 26% improvement to 4% worsening); 2 studies, 63 participants; very low-quality evidence, downgraded for imprecision, blinding, and attrition. We are unsure of an important improvement, as the results were inconclusive. Participants in Tai Chi programs were less likely than those in a control group to withdraw from studies at 8 to 12 weeks (19/180 in intervention groups versus 49/165 in control groups; risk ratio (RR) 0.40 (95% CI 0.19 to 0.86); absolute difference 17% fewer (95% CI 30% fewer to 3% fewer); 7 studies, 289 participants; low-quality evidence, downgraded for imprecision and blinding. There were no data available for radiographic progression. Short-term adverse events were not reported by group, but in two studies there was some narrative description of joint and muscle soreness and cramps; long-term adverse events were not reported. Authors’ conclusions It is uncertain whether Tai Chi has any effect on clinical outcomes (joint pain, activity limitation, function) in RA, and important effects cannot be confirmed or excluded, since all outcomes had very low-quality evidence. Withdrawals from study were greater in the control groups than the Tai Chi groups, based on low-quality evidence. Although the incidence of adverse events is likely to be low with Tai Chi, we are uncertain, as studies failed to explicitly report such events. Few minor adverse events (joint and muscle soreness and cramps) were described qualitatively in the narrative of two of the studies. This updated review provides minimal change in the conclusions from the previous review, i.e. a pain outcome.