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Low levels of the vitamin D-regulated antimicrobial peptide cathelicidin (LL-37) may negatively impact the immune status of human immunodeficiency virus-1 (HIV-1) infected individuals (HIV+). We compared plasma LL-37 levels in healthy controls (HIV−) and HIV+ individuals on or off antiretroviral therapies (ARTs) (ART+ and ART−, respectively), and evaluated the relationship between vitamin D and LL-37 levels. In this cross-sectional study, levels of LL-37, 25-hydroxycholecalciferol [25(OH)D3] and 1,25-dihydroxycholecalciferol [1,25(OH)2D3] were measured from an initial cohort of 18 healthy controls and 10 HIV+/ART− individuals. Because this cohort lacked HIV+/ART+ subjects, LL-37 was also quantified from a second cohort of 10 HIV+/ART− and 13 HIV+/ART+ individuals. LL-37 levels were significantly lower in the HIV+/ART− group compared to the healthy controls (P=0.01). A direct relationship was observed between LL-37 and both 25(OH)D3 and 1,25(OH)2D3. The level of 25(OH)D3 was predictive of higher LL-37 (P=0.04) and for any given level of 25(OH)D3, HIV+/ART− subjects averaged 20 % lower LL-37 compared to the healthy controls (P=0.045). For any given level of 1,25(OH)2D3, HIV+/ART− subjects averaged 25 % lower LL-37 compared to the healthy controls (P=0.018), although 1,25(OH)2D3 was not predictive of higher LL-37 (P=0.28). Finally, LL-37 levels were significantly lower in the HIV+/ART− group compared to the HIV+/ART+ group from the second cohort (P=0.045). Untreated HIV infection may contribute to lower LL-37 levels, independent of vitamin D levels. ART treatment may potentially mitigate this decrease in LL-37 levels.