Background: Monocytes (MO) are a heterogeneous population of myeloid cells defined into 3 distinct subsets based on CD14 and CD16 expression as classical (CD14highCD16-), non-classical (CD14lowCD16++) and an intermediate (CD14highCD16+) subset. It is suggested that CD16 expressing MO subsets patrol the periphery, migrate into tissues and display pro-inflammatory features. Our previous work identified CD16 expressing MO harboring HIV DNA appear to serve as a correlate to HIV-associated neurocognitive disorders (HAND) in chronic HIV infection. MO changes that occur in the earliest stages of HIV infection may be mechanistically relevant to the persistence of cognitive complications in patients despite suppressive antiretroviral therapy (ARV). Methodology: We characterized MO inflammatory phenotype and functional responses (IL-6, IL-1β and TNF-α) by a novel multiparametric flow cytometric technology in a prospective study of 17 ART-naive acute HIV-infected (AHI) individuals, captured during a hyper-acute window during Fiebig stage I (RNA+/ HIV IgM-, n=10) and III (HIV IgM+/IgG-, n=7) before appreciable antibody response can be measured and correlated to clinical parameters of disease progression (eg: plasma HIV Viral load). Wilcoxon rank sum tests were conducted to compare the differences between Fiebig stages. Results: We observed that subjects captured in Fiebig I had lower plasma HIV viral load compared to subjects in Fiebig III: median (Interquartile range) = 4.3 log10 copies/ml (3.6,5.4) vs 5.5 log10 copies/ml (5.4,7.5); p=0.01). Cross-sectionally, Fiebig I subjects had a greater frequency of only non-classical MO compared to Fiebig III (18.2% (8.7,26.9) vs 7.4 %(4.4,12.1); p=0.03). Lipopolysaccharide (LPS) stimulated IL-6+ MO responses were greater in Fiebig I compared to Fiebig III (14.5% (7.7,17.7) vs 5.3% (4.9,9.3); p=0.04). No differences in either basal or LPS stimulated IL-1β or TNF-α MO responses was seen between Fiebig stages. Plasma HIV viral load was inversely associated with both basal (r=-0.603;p=0.008) and LPS (r=-0.562; p=0.015) stimulated IL-6+ MO responses. Conclusions: These results indicate that the presence of HIV soon after infection differentially alters the inflammatory profile of various MO subsets and precedes peak viremia in AHI. Tracking MO inflammation after early institution of ARV therapy in AHI may have significant implications in reducing HAND.