This prospective, multicentre, randomized, double-blind and placebo controlled study was performed to describe the natural course of uncomplicated lower urinary tract infection (UTI). A total of 1143 women 18 y and above, consulting at 18 primary health care centres in northern Sweden for symptoms suggestive of UTI were included. The symptoms urgency, dysuria, suprapubic pain and loin pain were registered, and urine cultures performed at inclusion and follow-up visits 8-10 d and 5-7 weeks later. Associations between all symptoms and bacteriuria or bacterial counts were unpredictable. Eradication of symptoms and bacteriuria and combinations of them were studied in 288 patients placebo treated for 7 d, of whom 39% dropped out after the first follow-up visit. The spontaneous cure rate of symptoms was 28% after the first week, and 37% had neither symptoms nor bacteriuria after 5-7 weeks. Considering the high dropout rate after the first follow-up visit, the spontaneous cure rate of symptoms and bacteriuria was calculated to 24% at the end of study. We conclude that patient near-laboratory tests are required to establish the diagnosis of lower UTI, and the guidelines for diagnosis of UTI need to be revised.