The prevalence and duration of rectal and vaginal colonization with P- and F-fimbriated Escherichia coli and the relationship of colonization with these strains to blood group secretor status was investigated. Rectal and vaginal E. coli isolates were prospectively collected twice monthly for 6 months from 20 young women with and 20 without a history of recurrent urinary tract infection (UTI). Rectal and vaginal colonization with P- and/or F-fimbriated E. coli was highly prevalent. Nonsecretors who developed UTI during the study period were significantly more likely to be colonized rectally with F-fimbriated E. coli than were the infected secretors (56% vs. 27%; P = .042) or uninfected nonsecretors (56% vs. 31%; P = .046). Persistent vaginal and rectal E. coli colonization with fimbriated organisms occurred commonly in the study patients but was not often temporally associated with the development of UTI. Results suggest that nonsecretors are more susceptible than secretors to colonization with F adhesin-bearing E. coli isolates.