The sexual behaviour of 400 women with and 400 women without bacterial vaginosis from a health screening programme was investigated by a questionnaire to see if women with bacterial vaginosis had similar behaviours to women considered at risk for STDs. These patients were randomly selected from computer records. Eight hundred questionnaires were distributed and 641 women answered. The age of first sexual intercourse was lower among women with bacterial vaginosis (17.8 years) than those without (18.6 years; P less than 0.001). Number of lifetime sexual partners was higher among women with bacterial vaginosis (P less than 0.001). Women with bacterial vaginosis smoked or had smoked more often. These results indicate that women with bacterial vaginosis have similar sexual behaviour to those at risk for STDs.