To map the context of HIV in closed settings in Papua New Guinea (PNG), semi-structured interviews were undertaken with 56 prisoners and detainees and 60 key stakeholders. The nature of HIV-related risk differs for detained women and men, and reflects important gender-based issues present in PNG society more broadly. Women in detention are vulnerable to sexual violence and exploitation and at greatest risk of HIV while detained in police holding cells, where they are typically supervised by male officers, in contrast to prisons, where they have little contact with male staff. HIV risk for men in prison is associated with consensual and non-consensual sex; this risk is perpetuated by a pervasive culture of denial and institutionalised homophobia. The illegal nature of sodomy and male-to-male sex provides Correctional Services the legal grounds by which to refuse access to condoms for prisoners. Addressing HIV risk among detained men and women in PNG requires the reform of legislation, police and prison practices and an understanding of broader structural problems of gender-based violence and stigma and discrimination.