The aims of the study were to estimate the prevalence of bacteriuria in a female urban population, to follow up the same population over the years, and to relate bacteriuria to long-term prognosis with respect to mortality and kidney disease. The study was based on a randomly selected population sample comprising 1462 women aged 38-60 years at entrance to the study in 1968-69 with an initial participation rate of 90.1%. Bacteriuria was observed in 3-5%, increasing with age, and most often asymptomatic. Bacteriuria on one occasion meant increased risk of having bacteriuria 6 and 12 years later. The percentages of different types of bacteria and the resistance pattern were similar initially and at follow-up studies after 6 and 12 years. There were no differences in mortality or incidence of severe kidney disease during a 24-year follow-up between those with and those without bacteriuria in the baseline study.