Over three-fourths of human immunodeficiency virus (HIV)–infected men who have sex with men (MSM) have at least one herpesvirus detected in their semen, and cytomegalovirus (CMV) is the most prevalent. The presence of CMV is associated with higher T-cell immune activation and with HIV disease progression in treated and untreated individuals. In this study of 113 antiretroviral (ART)–naive HIV-infected MSM, we found that CMV replication in blood and semen was associated with higher levels of HIV DNA in peripheral blood mononuclear cells. These observations suggest that interventions aimed to reduce CMV replication and, thus, systemic immune activation could decrease the size of the latent HIV reservoir.