A cross-sectional study was designed to assess safe sexual behaviour among heterosexual couples after the woman learned of her partner's infection with HIV. Female partners who had known their partners' serostatus for at least 4 weeks were eligible for participation. Couples were interviewed separately and independent predictors of safe sexual behaviour were identified using multiple logistic regression. Safe sexual behaviour was defined as no unprotected vaginal, oral, or anal intercourse. Of 328 women, 197 (60%) reported safe sexual behaviour since learning of their partners' infection. Significant independent predictors of safe sexual behaviour included older women (>30 years old) (odds ratio [OR]=1.89; 95% confidence intervals [CI]=1.01-3.51), current negative HIV serostatus (OR=2.72; 95% CI=1.50-4.94), advanced clinical stage of the index case (OR=1.96; 95% CI=1.07-3.59), longer duration of relationship (10+ years) (OR= 2.35; 95% CI=1.15-4.82), fewer sex contacts (<100) (OR=2.01; 95% CI=1.14-3.56), only one lifetime partner (OR=2.29; 95% CI=1.26-4.17), non-smoking (OR=2.67; 95% CI=1.43-4.99), not practising oral sex (OR=3.35; 95% CI=1.82-6.19) and previous HIV testing (OR=2.11; 95% CI=1.09-4.07). In addition, women who had known their partner's infection for longer were less likely to report safe sexual behaviour (P < 0.001). Our results indicate that among female partners of HIV-positive Brazilian men, learning of their partner's infection does not uniformly result in safe sexual behaviour. Counselling must emphasize disclosure of serostatus to female partners and target couples with short-term relationships, as well as those where the woman has known about her male partner's infection for a long time, because these are the least likely to maintain safe sexual behaviour.