A national household survey of a representative sample of 9,984 individuals aged 15 years or over, carried out in 1996 using a combination of face-to-face interviews and self-completion questionnaires, was analyzed in order to describe the frequency of HIV sexual risk behaviours and condom use in Spain. Of a total of 8,101 persons (81%) who completed the questionnaire, 37% reported no sexual partner during the previous 12 months, 57% reported one partner and 6% reported more than one partner. Three per cent reported engaging in HIV sexual risk behaviour (i.e. more than one partner and failure to use a condom systematically), a pattern of behaviour which showed independent positive association with the male sex, an age of 20-59 years and being unmarried. Among those who had casual sexual partners during the preceding 12 months, 38% had always used condoms. In the multivariate analysis, failure to use a condom systematically with casual partners was associated with a higher age and being married. Of those who had regular partners during the previous 12 months, 26% had always used condoms, a finding associated with a lower age, higher educational level, unmarried status and non-cohabitation with the sexual partner. This survey has furnished some useful indicators for prevention purposes. Periodic repetition of this survey would enable possible changes in sexual risk behaviours to be detected.