We conducted a 6-month open-label trial in which 10 patients with active psoriatic arthritis received 2 micrograms of oral 1,25-dihydroxyvitamin D3 daily. Statistically significant improvement was noted in the tender joint count and physician global impression. Of these 10 patients, 4 had substantial (greater than or equal to 50%) improvement, and 3 had moderate (greater than or equal to 25%) improvement in the tender joint count. Two patients were unable to receive therapeutic doses because of hypercalciuria. High-dose vitamin D may be a useful therapeutic agent for psoriatic arthritis.