Extended-spectrum cephalosporins (ESC) are an important drug class for treating severe Salmonella infections. We screened the human collection from the National Antimicrobial Resistance Monitoring System 2000 for ESC resistance mechanisms. Of non-Typhi Salmonella tested, 3.2% (44/1,378) contained blaCMY genes. Novel findings included blaCMY-positive Escherichia coli O157:H7 and a blaSHV-positive Salmonella isolate. CMY-positive isolates showed a ceftriaxone MIC > or =2 microg/mL.