Background: Topical corticosteroids and calcipotriol have been used separately for many years to treat psoriasis. A new combination ointment has been formulated, which contains both calcipotriol and the corticosteroid betamethasone dipropionate. Objective: To compare the combination ointment with betamethasone dipropionate ointment, calcipotriol ointment and ointment vehicle in patients with psoriasis vulgaris. Methods: 1,603 patients were randomised to one of the 4 double-blind treatments used once daily for 4 weeks. Results: Themean percentage change in the PASI at the end of treatment was –71.3 (combination), –57.2 (betamethasone), –46.1 (calcipotriol) and –22.7 (vehicle). The mean difference of combination minus betamethasone was –14.2 (95% CI: –17.6 to –10.8, p < 0.001), of combination minus calcipotriol –25.3 (95% CI: –28.7 to –21.9, p < 0.001) and of combination minus vehicle –48.3 (95% CI: –53.2 to –43.4, p < 0.001). 6.0% of patients (combination) reported local adverse reactions compared to 4.9% (betamethasone), 11.4% (calcipotriol) and 13.6% (vehicle). Conclusion: Calcipotriol/betamethasone dipropionate combination ointment used once daily is well tolerated and more effective than either active constituent used alone.