Vitamin D deficiency is a common cause of morbidity. We prospectively studied 224 consecutive female patients in order to evaluate the prevalence of vitamin D deficiency and to assess the utility of various clinical and biochemical markers in predicting the deficiency. All of them were outpatients, 30 years old or older, and were evaluated from October 2006 through March 2008. Levels of 25 OH vitamin D > 30 ng/ml were considered sufficient. Mild deficiency was considered between 20 and 30 ng/ml and severe deficiency < 20 ng/ml. The mean age was 58 +/- 12.9 years; 77% were menopausal. Twenty nine percent of the patients had mild deficit and 26.8% had severe deficit of the vitamin. Severe deficit was associated with increasing age (62 vs. 56 years, p = 0.003), absence of sun exposure (25.82 ng/ml vs. 31.7 ng/ml, p < 0.005), obesity (70 vs. 61 kg, p < 0.05), absence of physical activity (27.8 ng/ml vs. 31.04 ng/ml, p = 0.0007) and slightly low levels of serum calcium (9.26 mg/dl vs. 9.51 mg/dl, p 0.01). We did not find any association between smokers and non-smokers patients, levels of serum phosphorus, creatinine and TSH. Vitamin D deficiency is a common disorder. It correlates with older age, absence of physical activity, sun exposure, obesity and slightly low levels of serum calcium. Improving diagnosis of this condition may enable us to improve the management of this disease.