Background: Psoriasis is a common disease of the skin. Metabolic disorders have been suggested in the etiology of psoriasis. Objective: As hypocalcemia has been reported to provoke psoriasis, we studied the blood calcium level in this disease. Patients and Methods: In this case-control study, we measured blood calcium level in 120 psoriatic patients visited in outpatient clinic or admitted in Ghahem Hospital in Mashhad and compared to 120 age and sex matched normal controls. Results: Considering blood calcium level of 8.5-10.5 mg/dl as normal, 17 psoriatic patients (14%) and 6 controls (5%) were hypocalcemic (P<0.05). Conclusion: As hypocalcemia in psoriatic patients was significantly more common in this study, estimation of blood calcium level is recommended in psoriasis.