OBJECTIVE To compare the effectiveness and toxicity of cyclosporin A (CsA) vs low-dose methotrexate (MTX) over a period of one year in the treatment of psoriatic arthritis (PsA) with peripheral involvement. METHODS Thirty-five patients with PsA were enrolled in a prospective, controlled, randomized trial. CsA was initially given in doses of 3 mg/kg/day to a maximum permitted dose of 5 mg/kg/day; MTX was given in oral doses of 2.5 mg every 12 hours for 3 consecutive doses each week up to a maximum dose of 15 mg/weekly. Clinical and laboratory evaluations were performed at entry and monthly thereafter. RESULTS After 6 and 12 months the number of painful joints, the number of swollen joints, the Ritchie index, the duration of morning stiffness, grip strength, CRP, the patient's and the physician's assessment of PsA activity, as well as the PASI, were significantly improved in both treatment groups. ESR values were significantly reduced only in the MTX group (p < 0.01), which also showed a significantly increase of liver enzymes. The changes in the main clinical and laboratory parameters during the course of CsA or MTX treatment were not significantly different except for the AST and ALT levels (p < 0.05). After one year of therapy CsA and MTX were withdrawn in 41.2% and 27.8% of the patients respectively, but these differences were not statistically significant. CONCLUSIONS Our one-year prospective trial shows that low-dose CsA and MTX are both effective in the treatment of PsA, but the differences in the tolerability of these drugs must be considered at the start of therapy.