Nineteen selected patients with severe, mostly systemic onset, juvenile rheumatoid arthritis were treated with methotrexate (MTX) for an average of 10.5 months. Twelve patients showed statistically significant improvement, as measured by the number of affected, swollen, tender, and functionally impaired joints, and by decreases in erythrocyte sedimentation rate and C-reactive protein and an increase in hemoglobin level. Systemic manifestations improved in 6 of 8 patients. In 10 children receiving corticosteroids, the dosage was reduced. Seven patients did not respond to MTX therapy. Six of them showed an unchanged disease course, and 1 had a relapse after 4 months of MTX treatments. Probable side effects included gastrointestinal symptoms, elevated liver enzymes, and herpes zoster infection. MTX treatment should be considered for children with life-threatening or severe disabling arthritis that is unresponsive to other therapy.