Questionnaires were administered to 122 urban black mothers of teenagers in order to: (i) understand aspects of their sexual behaviour and knowledge of the acquired immunodeficiency syndrome (AIDS); and (ii) assess their communication with their teenage children with regard to AIDS and sexual behaviour. The subjects comprised a 12.5% random sample of all houses in Lamontville, a black township south of Durban. The level of AIDS knowledge among mothers was high, while their sexual behaviour, characterised by a high pregnancy rate and a high proportion who have had children by more than one consort, placed them at high risk of acquiring human immunodeficiency virus (HIV) infection. No mother had experienced sexual intercourse during which her partner used a condom. Communication with their teenage children was poor; none of the mothers had spoken with them about AIDS and 89.3% had not discussed contraceptive methods with their teenage children. We found that urban black mothers were at high risk of acquiring HIV and, despite their knowledge of the modes of transmission and prevention of HIV infection, they had not begun using condoms as a risk-reducing measure, nor had they communicated the risk of unprotected sex to their teenage children. We recommend that AIDS intervention strategies should not concentrate only on passing on knowledge but also on providing women with the communication skills to negotiate the use of condoms with their partners and to convey the risk of HIV infection to their teenage children.