Context: People infected with HIV have a higher risk for developing insulin resistance, diabetes, and cardiovascular disease than the general population. Dipeptidyl peptidase IV (DPP4) inhibitors are glucose-lowering medications with pleiotropic actions that may particularly benefit people with HIV, but the immune and virological safety of DPP4 inhibition in HIV is unknown. Objective: DPP4 inhibition will not reduce CD4+ T lymphocyte number or increase HIV viremia in HIV-positive adults. Design: This was a randomized, placebo-controlled, double-blind safety trial of sitagliptin in HIV-positive adults. Setting: The study was conducted at an academic medical center. Participants: Twenty nondiabetic HIV-positive men and women (9.8 ± 5.5 years of known HIV) taking antiretroviral therapy and with stable immune (625 ± 134 CD4+ T cells per microliter) and virological (<48 copies HIV RNA per milliliter) status. Intervention: The intervention included sitagliptin (100 mg/d) vs matching placebo for up to 24 weeks. Main Outcome Measures: CD4+ T cell number and plasma HIV RNA were measured every 4 weeks; fasting serum regulated upon activation normal T-cell expressed and secreted (RANTES), stromal derived factor (SDF)-1α, Soluble TNF receptor II, and oral glucose tolerance were measured at baseline, week 8, and the end of study. ANOVA was used for between-group comparisons; P<.05 was considered significant. Results: Compared with placebo, sitagliptin did not reduce CD4+ T cell count, plasma HIV RNA remained less than 48 copies/mL, RANTES and soluble TNF receptor II concentrations did not increase. SDF1α concentrations declined (P < .0002) in the sitagliptin group. The oral glucose tolerance levels improved in the sitagliptin group at week 8. Conclusions: Despite lowering SDF1α levels, sitagliptin did not adversely affect immune or virological status, or increase immune activation, but did improve glycemia in healthy, nondiabetic HIV-positive adults. These safety data allow future efficacy studies of sitagliptin in HIV-positive people with cardiometabolic complications.