Forty women aged 18 to 40 years, attending the outpatient clinics of the Department of Internal Medicine of the University of Messina, Messina, Italy, for primary dysmenorrhea were enrolled. Patients were included if (1) their menstrual cycles lasted 21 to 35 days, with menstruation lasting 3 to 7 days; (2) they experienced at least 4 consecutive painful periods in the past 6 months with the pain starting one day before or on the day of onset of bleeding; (3) they showed a 25(OH)D serum level, measured with high-performance liquid chromatography, below the upper limit of the lowest quartile (<45 ng/mL) (to convert to nanomoles per liter, multiply by 2.496) obtained by dividing the normal range of our laboratory (20-120 ng/mL) into 4 parts. Patients had to be in good health and taking no medications including calcium, vitamin D, and oral contraceptives. Previous and current use of intrauterine contraceptive devices within the 6 months prior to enrollment was not permitted. During the observation period, patients used an accepted means of birth control. Use of NSAIDs was permitted and it had to be recorded in a sheet given to each woman.