This paper presents findings from a qualitative study of household and community responses to HIV/AIDS in Mexico. Fieldwork took place in two contrasting settings: (a) Ciudad Netzahualcóyotl, a socially marginalized urban community and (b) the homosexual community of Mexico City, a sexually marginalized social network. 113 in-depth interviews were conducted with people with HIV/AIDS, their relatives and members of their social networks. This paper describes findings from interviews conducted with family members of persons with AIDS. Four stages of response are identified and characterized within each community: (i) life before AIDS, (ii) life during the discovery of AIDS, (iii) living with a person with AIDS and (iv) surviving those who have died from AIDS. The social marginalization of both communities is central in explaining how families respond to the disease. In Ciudad Netzahualcoyotl, social support derives from a local culture of kinship. In the gay community, on the other hand, solidarity arises out of friendship. Between social support and discrimination, many more "ambivalent" behaviours (neither fully supportive nor discriminating) are displayed by family members and friends. Fear, pre-existing family conflicts and prejudice nurture these negative responses. Family responses and the processes to which they give rise, also differ depending on whether or not a male or female household member is affected. Policy recommendations are made concerning how best to promote positive family and household responses to persons with HIV/AIDS and how to inhibit negative ones.