To assess the efficacy and safety of golimumab in patients with active psoriatic arthritis (PsA). Adult patients with PsA who had at least 3 swollen and 3 tender joints and active psoriasis were randomly assigned to receive subcutaneous injections of placebo (n = 113), golimumab 50 mg (n = 146), or golimumab 100 mg (n = 146) every 4 weeks through week 20. Efficacy assessments through week 24 included the American College of Rheumatology 20% improvement criteria (ACR20), the Psoriasis Area and Severity Index (PASI) in patients in whom at least 3% of the body surface area was affected by psoriasis at baseline, the Short Form 36 Health Survey (SF-36), the disability index of the Health Assessment Questionnaire (HAQ), the Nail Psoriasis Severity Index (NAPSI), the physician's global assessment of psoriatic nail disease, and enthesitis (using the PsA-modified Maastricht Ankylosing Spondylitis Enthesitis Score [MASES] index). At week 14, 48% of all patients receiving golimumab, 51% of patients receiving golimumab 50 mg, and 45% of patients receiving golimumab 100 mg achieved an ACR20 response (the primary end point), compared with 9% of patients receiving placebo (P < 0.001 for all comparisons). Among the 74% of patients in whom at least 3% of the body surface area was affected by psoriasis at baseline, 40% of those in the golimumab 50 mg group and 58% of those in the golimumab 100 mg group had at least 75% improvement in the PASI at week 14 (major secondary end point), compared with 3% of placebo-treated patients (P < 0.001 for both doses). Significant improvement was observed for other major secondary end points (the HAQ and the SF-36), the NAPSI, the physician's global assessment of psoriatric nail disease, and the PsA-modified MASES index in each golimumab group compared with placebo. This efficacy was maintained through week 24. Golimumab was generally well tolerated. Treatment with golimumab at doses of 50 mg and 100 mg significantly improved active PsA and associated skin and nail psoriasis through week 24.