The study focused in sexual behaviour among socially excluded heroin users, identifying factors associated with inconsistent condom use. Data was collected in the cities of Granada and Seville between July and October 2000, through a structured questionnaire, to 391 participants. Twenty two and 15% of participants have made consistent use of condoms in vaginal sex in the last year with occasional and regular partners respectively. There is a greater likelihood of inconsistent condom use with occasional partners among users who had had oral sex, and who does not know if their partner(s) inject or injected drugs. For regular partners those who have an injecting partner and do not speak with their sexual partners about AIDS have a higher probability to do not use always a condom. For both groups, when always the partner is who propose the use of condoms (when used) and not themselves, the risk not to use it is near 4 times more than when themselves propose to use it. Speaking about condoms and AIDS with mate, partners and family, and learning to negotiate the use of condoms seems to be the most important strategies to be approached for this sample, from the social and health care system in order to promote a protected sex.