BACKGROUND: Biologic therapies such as adalimumab, a tumour necrosis factor antagonist, are safe and effective in the treatment of moderate to severe chronic plaque psoriasis. OBJECTIVES: To compare a biologic agent with methotrexate, a traditional systemic agent, to define clearly the role of biologics in psoriasis. METHODS: Patients with moderate to severe plaque psoriasis were randomized to adalimumab (80 mg subcutaneously at week 0, then 40 mg every other week, n=108), methotrexate (7.5 mg orally, increased as needed and as tolerated to 25 mg weekly; n=110) or placebo (n=53) for 16 weeks. The primary efficacy endpoint was the proportion of patients achieving at least a 75% improvement in the Psoriasis Area and Severity Index (PASI 75) after 16 weeks. Safety was assessed at all visits through week 16. RESULTS: After 16 weeks, 79.6% of adalimumab-treated patients achieved PASI 75, compared with 35.5% for methotrexate (P<0.001 vs. adalimumab) and 18.9% for placebo (P<0.001 vs. adalimumab). Statistically significantly more adalimumab-treated patients (16.7%) than methotrexate-treated patients (7.3%) or placebo-treated patients (1.9%) achieved complete clearance of disease. The response to adalimumab was rapid, with a 57% improvement in mean PASI observed at week 4. Adverse events were similar across treatment groups. Adverse events leading to study discontinuation were greatest in the methotrexate group, primarily because of hepatic-related adverse events. CONCLUSIONS: After 16 weeks, adalimumab demonstrated significantly superior efficacy and more rapid improvements in psoriasis compared with either methotrexate or placebo.