A multiresistant, lactose-negative Escherichia coli O78:H10 was isolated from 19 patients in Greater Copenhagen over a period of 8 months. At least 14 cases were community-acquired. 18 isolates originated from urine cultures and 1 from a faecal sample. 13 patients were predisposed to urinary tract infection (UTI) and 11 patients showed clinical signs of UTI. This is the first report of E. coli O78:H10 causing human disease. The cluster was probably food-borne, but the source was not identified. This cluster of identical disease associated E. coli was only uncovered because of its multiresistance and lactose-negative phenotype.