Arthralgia is a common presenting symptom of many rheumatic diseases. Vitamin D deficiency may lead to progression of skeletal symptoms to definite disease in susceptible subjects. This study was conducted to determine the relationship between vitamin D deficiency and unexplained arthralgia. Patients with arthralgia not related to a definite clinical condition were selected prospectively among subjects presented to a rheumatology clinic. Serum 25-hydroxyvitamin D (25-OHD) was measured by ELISA method and levels less than 20 ng/ml were considered as deficient levels. Serum 25-OHD levels and proportion of 25-OHD deficiency was compared in patients versus control. The association of serum 25-OHD and arthralgia was assessed by calculation of odds ratio (OR) using regression analysis. 167 patients with mean age of 38 ± 13.3 and 283 controls with mean age of 42.6±14.37 years (P=0.001) were studied. In patients mean serum 25-OHD was lower and proportion of deficiency was higher (P=0.001 for both).Serum 25-OHD deficiency was associated with 3.01 times increased risk of arthralgia (OR=3.01, 95% CI, 2.0- 4.25, P=0.001). After adjusment for age and sex, the risk of arthralgia remained significan at OR= 2.71(95%CI, 1.79-4.11,P=0.001).The odds of arthralgia decreased with increasing serum 25-OHD from OR=3.48 (95% CI,197-6,P=0.001) at serum <10 ng/ml to 3.39 (95%CI,1.93-5.98, P=0.001) at 10-19.9; and 1.31 (95%CI, 0.69-2.5, P=0.42) at 20-29.9 ng/ml. These findings indicate significant association of vitamin D deficiency and arthralgia. Regarding vitamin D deficiency as an environmental factor for development or progression of rheumatic diseases, this study justifies identification and correction of vitamin D deficiency in patients with arthralgia.