The CAPRISA 004 trial assessed effectiveness and safety of a 1% vaginal gel formulation of tenofovir, a nucleotide reverse transcriptase inhibitor, for the prevention of HIV acquisition in women. A double-blind, randomized controlled trial was conducted comparing tenofovir gel with placebo gel in sexually active, HIVuninfected18 to 40 year-old women in urban and rural KwaZulu-Natal, South Africa HIV serostatus, safety,sexual behavior and gel and condom use were assessed at monthly follow-up visits for 30 months.