The purpose of this study is to determine if Infliximab is safe and effective in the treatment of psoriatic arthritis. Infliximab (Remicade) targets specific proteins in the body's immune system to help control the development of inflammation to help reduce painful disease.

This is a phase III, multicenter, randomized (patients are assigned different treatments based on chance), double-blind (neither the patient nor the physician knows whether drug or placebo is being taken, or at what dosage), placebo-controlled study designed to determine the safety and effectiveness of Infliximab in the treatment of patients with psoriatic arthritis. This is an experimental medical research study. A total of 200 people in North America and Europe participated in this study during the 17 month study period. Patients will receive infusions of either placebo or 5 or 10 mg/kg infliximab (Remicade) at weeks 0,2, 6, 14, 16, 18, 22, 30, 38, and 46. Safety evaluations will be performed at specified intervals throughout the study and will consist of laboratory tests, vital signs (such as blood pressure), physical examinations and the occurrence and severity of adverse events as well as other study specific procedures. Patients will receive either placebo or 5 mg/kg induction infusions (weeks 0, 2 and 6) followed by maintenance infusions every 8 weeks until week 46. In the placebo group, patients may early escape at week 16 and crossover at week 24 to infliximab;. In the 5mg/kg group, dose escalation if needed at week 38.

Inclusion Criteria:

• Diagnosed psoriatic arthritis for >= 6 months
• active arthritis with >= 5 tender and 5 swollen joints
• active psoriasis

Exclusion Criteria:

• Have other inflammatory diseases, including but not limited to, rheumatoid arthritis, ankylosing spondylitis, systemic lupus erythematosus, or Lyme disease
• Received any systemic immunosuppressives within 4 weeks prior to enrollment in the study