Vaginitis is one of the most common problems in clinical medicine, and it is the reason cited most often for visits to obstetricians and gynecologists. This article reviews the epidemiology in the United States and Scandinavia for the three major causes of vaginitis: candidiasis, trichomoniasis, and bacterial vaginosis. The incidence of candidiasis has increased dramatically during the past decade, with an increase in the percentage of non-albicans Candida strains. However, in Scandinavia the incidence of candidiasis has been relatively stable, between 10% and 30%, during the past 5 years. The incidence of Trichomonas has decreased dramatically in both the United States and Scandinavia during the past 15 years, partly attributable to the advent of metronidazole. In the United States bacterial vaginosis continues to be the leading variety of vaginal infection, affecting a broader spectrum of women than gonorrhea. The prevalence of bacterial vaginosis in Scandinavia is about 30%, and this percentage increases with age according to studies of patients at sexually transmitted disease clinics.