A multi-center open prospective research was conducted in order to assess the safety and efficacy of tacalcitol 20 microg/g ointment once daily (maximum 10 g/day) in the long-term treatment of psoriasis vulgaris. For the 74 subjects included in the 54-week efficacy analysis, the mean PASI score at the beginning of the study was 22.49 10.20 (mean SD), which was 5.73 6.04 after 54 weeks. A significant decrease (p < 0.001) in the mean PASI score was seen after 1 week of application, and the score remained almost constant after 18 weeks through 54 weeks. Twenty-five local adverse drug reactions were noticed in 16 of the 154 subjects included in the safety analysis. No increase in the incidence of severe adverse drug reactions was seen in the long-term administration of tacalcitol 20 microg/g ointment. Although a significant decrease in the intact parathyroid hormone (PTH) and 1alpha,25-(OH)2D3 was observed, the homeostasis of the corrected serum calcium was maintained. Tacalcitol 20 microg/g ointment, applied once daily at doses of up to 10 g/day (200 microg tacalcitol), is safe and effective, even in long-term administration, in the treatment of patients with psoriasis vulgaris. Serum calcium should be monitored in patients with decreased renal function and other suspected impairment of calcium metabolism, before and during the treatment with tacalcitol 20 microg/g ointment.