Researchers in Thailand conducted a cross-sectional study of 101 patients with systemic lupus erythematosus (SLE; mean age, 40.13 years; 96% women). Blood samples were collected and stored. Radioimmunoassay was used to measure levels of serum 25(OH) vitamin D (25[OH]D). Vitamin D deficiency and insufficiency were considered at 30 ng/mL and 20 ng/mL, respectively. After demographic, clinical and laboratory data were collected, univariate and multivariate linear regression analyses were used to examine their associations with 25(OH)D level.