To compare the effects of individualised exercises in a heated pool to similar exercises on land in people with rheumatoid arthritis (RA). Randomised controlled trial with concealed allocation and assessor blinding. Hospital rheumatology clinic in Birmingham, UK. 115 adult patients with RA meeting American College of Rheumatology criteria, invited to participate on referral for physiotherapy, by invitation in clinics, or by mail. Fifty-seven patients were randomised to water-based exercises and 58 to land-based exercises. Water-based exercises were performed in 35°C water in sessions with up to four patients. Land-based exercises were performed in sessions with up to six patients. Both groups performed joint mobility, muscle strength, and functional activities, tailored to each individual's ability. Both exercise programs consisted of weekly 30-min sessions for six weeks. Patients were not required to do exercises between treatment sessions but could do so if they chose. The primary outcome was self-rated overall effect of treatment, measured on the day treatment was completed on a 7-point scale ranging from 1 (very much worse) to 7 (very much better). Secondary outcomes included a visual analogue scale of pain, the health assessment questionnaire (HAQ), ten metre walk speed, and the EuroQol-5D questionnaire. Secondary outcomes were also collected at 3 months post treatment. At end of treatment 87% (40/46) of the patients treated with water-based exercise felt much better or very much better. This proportion of patients was significantly greater than the 47.5% (19/40) of patients in the land-based group with the same ratings (relative risk = 1.8, 95% confidence interval 1.3 to 2.6). Sensitivity analyses showed that this result was robust to different assumptions. There were no significant differences between groups in the change in pain, HAQ, ten metre walk speed, or EuroQol-5D either on the day treatment was completed or at 3 months follow-up. Patients with RA are more likely to report feeling much better or very much better immediately after treatment if they are treated with exercises in a heated pool compared to similar exercises on land. The duration of this perceived benefit is unclear.