Individual HIV risk estimates were generated from reported sexual behavior for 1,146 California Latino Couples Study participants (573 couples). These Bernoulli process model-based estimates proved strongly associated with individual sexually transmitted disease history. Mean estimated background risk from sexual contacts other than with their primary partner was substantially lower for the females than the males (1.4 vs. 7.4 per 10,000). After including their chance of infection from each other, mean net estimated risk was higher for the females than the males (9.2 vs. 8.6 per 10,000). Individual background risk was predicted by individual demographic and psychosocial characteristics (females: coefficient of concordance C = 0.84 predicting any (nonzero) risk; adjusted R(2) = 36% predicting level of risk, given any risk; males: C = 0.78; R(2) = 24%). Characteristics of women with higher risk primary partners were also identifiable (C = 0.65; R(2) = 13%). There was no significant negative association between the male partner's background sexual risk and the aggregate infectivity of the woman from him (taking into account the total number of their condom-protected and unprotected acts of different types).