Background: The scalp is a problematic area in psoriasis where treatment is often difficult. The lesions often extend beyond the hairline to involve the forehead, neck and sensitive facial skin. Topical corticosteroids and potentially irritant topical preparations have only limited utility in these sensitive areas. Most of the patients additionally suffer from psychosocial problems due to the visibility of lesions., Objective: The aim of this multicenter, prospective, randomized, double-blind study, was to assess efficacy, safety and tolerability of once daily tacalcitol emulsion (4 micro g/g) compared to placebo in the treatment of scalp psoriasis., Methods: To determine efficacy, safety and tolerability, 273 patients with mild to moderate scalp psoriasis were treated over a 8-week period. Response to treatment was evaluated using the sum score of erythema, infiltration and scaling. Global improvement of psoriasis was rated by the investigators and the patients using a 5-point scale. In addition the single scores of erythema, infiltration and scaling were assessed by the investigators, and the patients were asked to evaluate the intensity of itching and scaling over the treatment period., Results: Tacalcitol was significantly superior to placebo in reducing the severity of scalp psoriasis. At the end of the study, the median sum score decreased by 53% in the tacalcitol group and was significantly better than placebo with 30% (p<0.0001). Global assessment of improvement was significantly greater in the tacalcitol group in both investigator and patient evaluation. 80% of patients on tacalcitol showed improvement to clearance and was statistically significant better than placebo (p <0.0001) in the investigator rating after 8 weeks. Tacalcitol was significantly superior to placebo in reducing erythema, scaling and infiltration, and in the patient assessment in reducing scalp scaling and itching. Treatment was very well tolerated. Local reactions were transient and uncommon. Their incidence was similar in both treatment groups. No serious side effects were reported, including those relating to calcium homeostasis or vitamin D(3) metabolism. No changes in mean levels of serum calcium, parathyroid hormone (PTH), calcitriol and in 24h-urinary excretion were observed., Conclusion: The results of this study indicate that topical application of tacalcitol (4 micro g/g) emulsion once daily is an effective, safe and very well- tolerated treatment for scalp psoriasis.