Although nail psoriasis occurs frequently in patients with psoriatic skin lesions, effective treatments are limited. Occurrence of nail psoriasis by type and incidence of nail clearance using the Nail Psoriasis Severity Index were evaluated. This was a 50-week, phase III study in which 378 patients with moderate to severe psoriasis were randomized 4:1 to infliximab (5 mg/kg) or placebo at weeks 0, 2, 6, and every 8 weeks through week 46, with placebo crossover to infliximab at week 24. Of the 373 evaluated patients, 305 (81.8%) had baseline nail psoriasis. The right thumbnail was most often the worst involved nail, and pitting and onycholysis were the most common lesions. Among patients with baseline nail psoriasis, 6.9%, 26.2%, and 44.7% in the infliximab group had nail disease clearance at weeks 10, 24, and 50, respectively, versus 5.1% in the placebo group at week 24 (P < .001). Mean percent improvements in Nail Psoriasis Severity Index score at weeks 10 and 24 were 26.8% and 57.2%, respectively, in the infliximab group versus -7.7% and -4.1%, respectively, in the placebo group (both P < .001). At week 24, mean percent improvements in nail matrix and nail bed features were 52.9% and 69.2%, respectively (vs -1.9% and 18.4% for placebo; P < .001). The study did not evaluate nail response beyond 1 year. Patients with psoriasis receiving infliximab experienced marked and sustained nail improvement.