The therapeutic efficacy of intermittent, monthly, postmenstrual prophylaxis with a single 500 mg clotrimazole vaginal tablet (n = 33) was compared with placebo tablets (n = 29) in 62 woman (age 28.1, SD 7.2 years) with recurrent vulvovaginal candidiasis. The number of episodes of acute vulvovaginal candidiasis experienced during the year prior to inclusion was 6.3, SD 1.9. The cumulative recurrence frequency after 6 months intermittent prophylaxis with clotrimazole (30.3%) was lower (p less than 0.001) than that recorded for the women who received placebo (79.3%). After an additional 6 months observation period without treatment there was no significant difference in the cumulative recurrence frequency between the groups (clotrimazole 84.9%; placebo 86.2%). The vagina was recolonised with Candida albicans in 70% of the women after 6 months prophylactic treatment with clotrimazole and in 86% of the women who had received placebo. Thus, this study has demonstrated that postmenstrual prophylactic treatment with a single 500 mg clotrimazole vaginal tablet, applied monthly, prevents recurrence of symptoms, although it does not eliminate yeasts from the vagina.