Recent reports suggest a role of hypovitaminosis D in the pathogenesis of inflammatory autoimmune diseases (ARD); we investigated 25(OH)vitamin D plasma level before and after supplementation in ARD and NARD (non-ARD: osteoporosis and/or OA) patients. We retrospectively evaluated 572 consecutive clinical records of adult patients at immuno-rheumatology and rehabilitative units of our institution from January 2006 to October 2009. We excluded patients with vitamin D supplementation or renal failure, primary hyperparathyroidism, liver failure. We recorded 25(OH)vitamin D plasma concentration of 245 patients together with other clinical data. We then evaluated 25(OH)vitamin D plasma concentration of 100 (43 ARD and 57 NARD) patients previously included who underwent 750-1,000 UI/die 25(OH)vitamin D supplementation for at least 6 months. Appropriate statistical analysis was performed. The median 25(OH)vitamin D concentration was not significantly different between 119 ARD [33.4 (IQR 22.5-54.9) nmol/l] and 126 NARD patients 32.9 (IQR 18.7-50.2). In stepwise logistic regression, female sex (F:13.7), winter-spring season (F:5.6) and older age (F:5.3), but not ARD, predicted plasma 25(OH)vitamin D <75 nmol/l. Cholecalciferol supplementation increased 25(OH)vitamin D plasma concentration equally in both ARD and NARD; however, only 29/100 patients reached a plasma level ≥75 nmol/l without differences between ARD and NARD (χ(2) = n.s.). Hypovitaminosis D is common in rheumatic patients. Sex and age but not ARD are risk factors for this condition. 750-1,000 UI/die of cholecalciferol is not sufficient to normalize plasma level in these patients. Increase of plasma 25(OH)vitamin D after treatment is not influenced by the presence of an inflammatory autoimmune disease.