To obtain evidence concerning short-term and long-term efficacy of clinical and health status measures in rheumatoid arthritis (RA), we conducted two observational studies--a 6-month study of 233 patients receiving methotrexate and a 10-year study of 157 patients receiving multiple treatments in a rheumatic disease clinic. Results of the 6-month study yielded effect sizes for treatment similar to the meta-analyses reported by Felson [corrected] et al. (Arthritis Rheum 33:1449-1461, 1990) and the controlled trials of methotrexate reported by Weinblatt et al. (Arthritis Rheum 33:330-338, 1990), suggesting that observational studies provide valid measurements of treatment effect. The effect size for the Health Assessment Questionnaire (HAQ) was 0.5. By contrast, the 10-year study suggested that standard clinical variables changed little and were not useful in assessing RA outcome, while the effect size of the HAQ was -2.39. These data continue to underscore the differences between short-term trials and the long-term outcome of RA, and suggest an important place for the HAQ or similar instruments in all phases of RA evaluation and assessment.