The characteristics of Escherichia coli isolated from the urine in 178 consecutive episodes of community-acquired cystitis in adult women were studied and compared with strains isolated from stools of 287 healthy adults. The prevalence of each of the previously described virulence-associated factors for urinary tract infection was significantly higher in the cystitis than in the stool isolates. The figures were 25.3% and 10.8%, respectively, for P fimbriation; 19.7% and 1% for Non-P MR adhesins, 13.5% and 7.3% for type 1C fimbriae and 22.5% and 10.8% for hemolysin production. 54% of the cystitis strains (but only 21.6% of the stool isolates) had at least 1 of these virulence-associated factors. These factors were mutually associated in a non-random manner; the association of P fimbriae with K1 and of Non-P MR adhesins and type 1C fimbriae with K5 capsules were highly significant. However, no clones specifically associated with cystitis could be identified. No significant differences were found between isolates from the first or recurrent UTI, or from younger or older, compromised or non-compromised patients. We conclude that P fimbriae, Non-P MR adhesins, type 1C fimbriae and hemolysin production all contribute to the establishment of cystitis in adults.