A retrospective review of methotrexate (MTX) treatment assessed the clinical course in 124 rheumatoid arthritis (RA) patients. After 5 years, 39 (31%) patients continued MTX with clinical benefit. Although patients continuing MTX after 5 years were younger (45 +/- 13 v 54 +/- 12 yrs, P less than .001) and had a shorter disease duration of RA (9.3 +/- 8.1 v 14 +/- 11 yrs, P less than .05) than patients who discontinue the drug, these differences were not considered clinically significant. MTX was discontinued in 20 patients for a lack of clinical benefit, in 21 patients for non-drug-related reasons, and in 44 patients for suspected adverse drug reactions. The adverse drug reactions requiring permanent discontinuation of MTX were nausea, stomatitis, hair loss, rash, pulmonary reactions, elevated liver enzymes, hematologic abnormalities, and hepatic fibrosis. At least one adverse drug reaction was reported by 115 (93%) patients receiving MTX, but the majority did not require permanent drug discontinuation. Although the prevalence of adverse reactions increased with longer duration of therapy, no differences existed in the type of reactions reported over 5 years of treatment. There were no risk factors identified that were clearly associated with the development of toxicity. Long-term therapy was primarily limited by adverse reactions rather than loss of efficacy.