The epidemiology of clavulanic acid-inhibited extended-spectrum beta-lactamases (ESBLs) was investigated among infection-associated enterobacterial isolates at the University Hospital in Lausanne, Switzerland, from January 2004 to June 2005. Out of 57 nonrepetitive ESBL producers (prevalence rate of 0.7%), 45 produced CTX-M-like ESBLs. CTX-M enzymes were mostly from clonally nonrelated Escherichia coli isolates, from urinary infections and community-acquired infections. Pediatric patients (20 out of 57) accounted for a large number of CTX-M producers. CTX-M-15 was the most frequent CTX-M-type enzyme. The plasmid-located bla(CTX-M) genes were associated with either ISEcp1 or ISCR1 insertion sequences. This study is the first published report of CTX-M-type beta-lactamases in Switzerland.