Background: Patients with HIV infection are at increased risk of cardiovascular disease (CVD). Vitamin D insufficiency has been associated with increased CVD risk in non-HIV populations. This study sought to determine the relationship between vitamin D status and markers of CVD and HIV-related factors in HIV-positive patients. Methods: Patients with HIV infection on antiretroviral therapy and healthy controls were prospectively enrolled. Fasting lipids, glucose, insulin, inflammatory markers (soluble tumour necrosis factor-α receptor I, interleukin-6 and high-sensitivity C-reactive protein) and endothelial markers (soluble intercellular adhesion molecule-1 and soluble vascular cell adhesion molecule-1) were measured. Fasting 25-hydroxyvitamin D (25(OH)D) was measured from stored serum samples. The internal carotid artery and common carotid artery (CCA) intima-media thickness (IMT) were measured in a subset of HIV-positive patients. Baseline cross-sectional data were analysed. Results: A total of 149 HIV-positive patients (56 with carotid IMT) and 34 controls were included. Controls had higher adjusted mean 25(OH)D levels than HIV-positive patients (P=0.02). In multivariable linear regression among the HIV-positive patients, 25(OH)D was positively associated with CD4+ T-cell restoration after antiretroviral therapy (ΔCD4 = current - nadir CD4+ T-cell; P<0.01), but was not associated with inflammatory or endothelial markers. In multivariable logistic regression, odds of having CCA IMT above the median were more than 10x higher in those with lower 25(OH)D levels (OR=10.62, 95% CI 1.37-82.34; P<0.01). Conclusions: Vitamin D status in HIV-positive patients was positively associated with improved immune restoration after antiretroviral therapy and negatively associated with CCA IMT. These findings suggest that vitamin D may play a role in HIV-related CVD and in immune reconstitution after antiretroviral therapy. ©2011 International Medical Press.