OBJECTIVE To investigate correlates of herpes simplex virus type 2 (HSV-2) DNA and HIV-1 RNA among women with genital ulcer disease (GUD). METHODS Baseline data from a randomized placebo-controlled trial of episodic herpes treatment in Ghana and the Central African Republic. METHODS GUD aetiology was determined by polymerase chain reaction (PCR) from a lesional swab. Real-time PCR was used to quantify HIV-1 RNA, and HSV-2 DNA in cervicovaginal lavages (CVL) and HIV-1 RNA in plasma. Genital infection was defined as the presence of virus in the lesion or CVL. RESULTS Of 441 women enrolled, 79.0% were HSV-2 seropositive, 46.6% were HIV-1 seropositive, and 50.0% had an HSV-2 ulcer. Among 180 HSV-2/HIV-1 co-infected women, cervicovaginal HIV-1 RNA was detected more frequently in women with HSV-2 ulcers (67.9%) or cervicovaginal HSV-2 DNA only (72.3%) compared with women without genital HSV-2 infection (42.4%) (P = 0.004). Women with genital HSV-2 infection had higher median cervicovaginal HIV-1-RNA loads (3.14 log10 copies/mL versus 2.10 log10 copies/mL; P = 0.003), higher plasma HIV-1-RNA loads (median 5.10 versus 4.65 log10 copies/mL; P = 0.07), and lower median CD4 cell counts) (198 versus 409 cells/mm, P = 0.03). Cervicovaginal HIV-1 RNA and HSV-2 DNA were significantly correlated after adjusting for plasma HIV-1 RNA and CD4 cell counts (P < 0.001) and a 10-fold increase in cervicovaginal HSV-2 DNA was associated with a 1.7-fold increase in plasma HIV-1 RNA (P = 0.003). CONCLUSIONS Genital HSV-2 infection is associated with increased cervicovaginal and plasma HIV-1 RNA among co-infected women with genital ulcers, independently of the level of immunodeficiency, highlighting the close interaction between these two viruses and the role of HSV-2 as a co-factor for the sexual transmission of HIV-1.