Background: The World Health Organization (WHO) is international public health’s major coordinating authority. The HIV/AIDS pandemic presents WHO with an unprecedented challenge. Over the past decade, the Cochrane HIV/AIDS Review Group (CRG) and WHO have collaborated several times on HIV/AIDS guideline development and policy setting. Objectives: Through working with WHO, to increase the use of the HIV/AIDS evidence-base in its policies and guidelines. Methods: WHO has a constant need to make and update its HIV/AIDS recommendations. On some occasions, WHO consulted informally with our CRG; on others, WHO formally commissioned us to assess the evidence for particular interventions. Results: In 2001, our review of nonoxynol-9 (N-9) for HIV prevention led WHO to conclude that N-9 should not be used. In the same year, WHO commissioned and funded a review of male circumcision for HIV prevention. In 2002, we presented our seven reviews of combination antiretroviral therapy, and WHO added these to its Model List of Essential Medicines. In 2006, our review of essential interventions for people living with HIV/AIDS contributed to new WHO guidelines. WHO recently adopted the GRADE approach in guideline development, leading to several new collaborations with our Group. We are currently compiling the evidence and creating GRADE profiles on the treatment and prevention of diarrhea and malaria in children with HIV, as part of the WHO compendium on comprehensive care of the HIV-infected child. In addition, we are helping WHO update its guidelines for adult antiretroviral therapy, also using the GRADE approach. Conclusions: Cochrane HIV/AIDS reviews are a crucial resource for WHO in setting policy and developing up-to-date, evidence-based guidelines on HIV/AIDS prevention, treatment and care. Through our work together we are closing the gap between WHO’s need for the best evidence to guide HIV/AIDS policy decisions, and the Cochrane HIV/AIDS Group’s ability to generate it.