In the Calgary Health Region during 2000-2003, prospective, active, population-based laboratory surveillance for all cefoxitin-resistant Escherichia coli isolates was performed. Isolates were screened with an inhibitor-based disk test, and plasmid-mediated types were identified by multiplex PCR with sequencing. A total of 369 AmpC beta-lactamase-producing E. coli isolates were identified; annual incidence rates were 1.7, 4.3, 11.2, and 15 per 100,000 residents for each year, respectively. AmpC beta-lactamase-producing E. coli was 5x more likely to be isolated from female than male patients across all age groups except < 1 year. Of these isolates, 83% were community onset, and urine was the principal site of isolation (90% of patients). PCR showed that 125 (34%) were positive for bla(cmy) genes; sequencing identified these enzymes to be CMY-2. In this large Canadian region, AmpC beta-lactamase-producing E. coli is an emerging community pathogen that commonly causes urinary tract infections in older women.