Some denialists, widely reviled, contend that HIV does not cause AIDS. Other denialists, widely respected, contend that HIV transmits so poorly through trace blood exposures that iatrogenic infections are rare. This second group of denialists has had a corrosive effect on public health and HIV programmes in sub-Saharan Africa. Guided by this second group of denialists, no African government has investigated unexplained HIV infections. Denialists have withheld and ignored research findings showing that non-sexual risks account for substantial proportions of HIV infections in Africa. Denialists have promoted invasive procedures for HIV prevention in Africa – injections for sexually transmitted infections, and adult male circumcision – without addressing unreliable sterilization of reused instruments. By denying that health care causes more than rare infections, denialists blame (stigmatize) HIV-positive African adults for causing their own infections through sexual behaviour. Denialism must be overcome to ensure safe health care and to combat HIV-related stigma in Africa.