To examine the changes in nutritional status during the progression of rheumatoid arthritis (RA), we studied anthropometric and biochemical variables in 97 Japanese patients with RA. Anthropometric data included body mass index (BMI), triceps skinfold thickness (TSF), and arm muscle area (AMA). Levels of albumin and cholesterol in serum, and lymphocyte count were studied as biochemical variables. The prevalence of malnutrition defined as hypoalbuminemia less than 3.4 g/dl was 24.7%, similar to the reports in other countries. Analysis of the data according to disease stage showed that malnutrition in RA was characterized by a progressive reduction in body protein. Body mass index and TSF were increased in patients with stage 1 disease, whereas serum albumin and AMA were within normal range. Stage 2 patients had normal BMI with decreased body protein, albumin, and AMA. Progression to stages 3 and 4 was associated with a stepwise decrease in AMA; serum albumin and BMI remained in the same range as stage 2. Albumin values and AMA were significantly lower in patients with poor functional class and high C-reactive protein. The characteristic progression of malnutrition in RA is attributed to excessive protein catabolism evoked by inflammatory cytokines and by disuse atrophy due to functional impairment.