Fasting is an effective treatment for rheumatoid arthritis, but most patients relapse on reintroduction of food. The effect of fasting followed by one year of a vegetarian diet was assessed in a randomised, single-blind controlled trial. 27 patients were allocated to a four-week stay at a health farm. After an initial 7-10 day subtotal fast, they were put on an individually adjusted gluten-free vegan diet for 3.5 months. The food was then gradually changed to a lactovegetarian diet for the remainder of the study. A control group of 26 patients stayed for four weeks at a convalescent home, but ate an ordinary diet throughout the whole study period. After four weeks at the health farm the diet group showed a significant improvement in number of tender joints, Ritchie's articular index, number of swollen joints, pain score, duration of morning stiffness, grip strength, erythrocyte sedimentation rate, C-reactive protein, white blood cell count, and a health assessment questionnaire score. In the control group, only pain score improved score. In the control group, only pain score improved significantly. The benefits in the diet group were still present after one year, and evaluation of the whole course showed significant advantages for the diet group in all measured indices. This dietary regimen seems to be a useful supplement to conventional medical treatment of rheumatoid arthritis.