The efficacy and safety of the novel DMARD leflunomide was compared to placebo and sulfasalazine in a randomized, double-blind study. At Week 24, leflunomide significantly reduced tender and swollen joint counts and physician and patient assessment scores compared to placebo (P < 0.001). Response rates with leflunomide were significantly greater than placebo: ACR 20% (55% vs 29%, P = 0.0001). Comparable response rates were observed with sulfasalazine (ACR 20%: 56%). Leflunomide significantly improved HAQ scores compared to placebo or sulfasalazine (P < 0.009). The onset of action with leflunomide was rapid and was seen as early as Week 2. Radiographic disease progression was significantly slower with leflunomide than placebo (P < 0.01). Leflunomide was well tolerated. No long-term safety issues were reported with leflunomide in patients who opted to continue treatment for up to 2 years. Efficacy of leflunomide in the treatment of RA was maintained at 2 years.