Seven clusters of hospital infection due to Salmonella enterica serovar typhimurium were documented in the neonatology clinic of a children's hospital between April 2002 and March 2004. Eighty-one neonates were infected. Three cases were asymptomatic, 73 cases had gastroenteritis as the only clinical condition, and 5 cases had bacteremia associated with gastroenteritis. All isolates from stool and blood samples (n=86) were identified as Salmonella enterica serovar typhimurium. Extended-spectrum beta-lactamase (ESBL) production was determined by clavulanate disk potentiation assay in all isolates. Enterobacterial Repetitive Intergenic Consensus polymerase chain reaction (ERIC-PCR) was performed in 26 selected isolates, which were chosen as being representative of different clusters, to determine the clonal relationship. PCR, isoelectric focusing and sequence analysis revealed the production of CTX-M-3, TEM-1 and SHV-12 by these isolates in 23%, 76.9% and 100%, respectively. None of the isolates had PER beta-lactamase production. Standard infection control measures such as handwashing and disinfection procedures were implemented in initial clusters. During the two-year period, the infection control policy of the hospital was improved with appropriate actions such as assignment of an infection control nurse and increasing the number of staff of the clinic, and finally, with the establishment of an active surveillance program, the clusters were stopped.