The aim of the study was to describe the prevalence and age distribution of bacterial vaginosis (BV) during an observation period of 15 years in a population study with cross-sectional samples of adult women living on the Åland Islands. The Åland Islands form an archipelago in the Baltic Sea and are a province of Finland. Every fifth year, specific age groups in the adult female population are invited to participate in a screening program for early diagnosis of cervical cancer using a papanicolaou (PAP)-stained vaginal smear. Women in the age groups of 20, 25, 30, 35, 40, 45, 50, 55, and 60 years are called each year. BV diagnosis of the PAP-stained smears uses the classification according to Nugent. The PAP-stained smears from the screening program of cervical cancer 1993, 1998, 2003, and 2008 were used in this study. A total of 3456 slides were investigated and 271 women could be followed for the 15-year observation period. The prevalence of BV declined from 15.6% in 1993 to 8.6% in 2008. The highest prevalence occurred among the age groups of 35 and 50 years. Among the 271 women who could be followed for the 15-year observation period, two-third showed normal ⁄ intermediate flora and one-third were infected with BV at least once. As this is a cross-sectional population study spanning 15 years, the prevalence of BV in the female adult population of the Åland Islands can be estimated. The prevalence has declined between 1993 and 2008 from 15.6% to 8.6%.