Objective: Resting-state functional connectivity MRI (rs-fcMRI) may provide insight into the neurophysiology of HIV and aging. Methods: In this cross-sectional study, we used rs-fcMRI to investigate intra- and internetwork connectivity among 5 functional brain networks in 58 HIV-infected (HIV+) participants (44% receiving highly active antiretroviral therapy) and 53 HIV-uninfected (HIV-) controls. An analysis of covariance assessed the relationship among age, HIV laboratory markers, or degree of cognitive impairment and brain networks. Results: Individuals who were HIV+ had decreased rs-fcMRI intranetwork correlations in the default mode (DMN, p = 0.01), control (CON, p = 0.02), and salience (SAL, p = 0.02) networks, but showed no changes in the sensorimotor (SMN) or dorsal attention (DAN) network. Compared with HIV-controls, participants who were HIV+ had a significant loss of internetwork correlations between the DMN-DAN (p = 0.02), trending loss in DMN-SAL (p = 0.1) and CON-SMN (p = 0.1), and trending increase in CON-SAL (p = 0.1). Neither HIV markers (plasma HIV viral load or CD4+ cell count) nor degree of cognitive impairment correlated with rs-fcMRI measures. Aging correlated with a decrease in the magnitude of intranetwork functional connectivity within the DMN (p = 0.04) and SAL (p = 0.006) and with decreased magnitude of internetwork functional connectivity between DMN and SAL (p = 0.009) for both HIV+ and HIV-participants. No interaction was observed between HIV and aging. Conclusions: HIV and aging may cause independent decreases in rs-fcMRI. HIV may lead to a baseline decrease in brain function similar to deterioration that occurs with aging.