OBJECTIVES: Conduct an cost effectiveness analysis of ertapenem in the treatment of enterobacteria producing beta-lactamases of extended spectrum (BLEES) sepsis at the Mexico Children's Hospital “Federico Gomez”. METHODS: Cost effectiveness analysis from the Children’s Hospital perspective and based in a decision model of static cohorts with the diagnosis of BLEES enterobacterial sepsis.  The comparators used were meropenem and imipenem, the time horizon was one year. To model the scenarios associated with the increase percentage of P. aeruginosa resistant to carbapenems, a 2% assumption was made based on the experience and feedback from the hospital’s infectologist  for the case in which the use of carbapenems are not changed.  These scenarios were compared to a scenario without the increase in the percentage. Treatment costs for carbapenems were calculated in a 10 day scheme for an average weight of 25 kg.  Treatment average cost for P. aeruginosa were obtained from patients charts. A univariate deterministic sensitivity analysis with a ±5% variation was performed. RESULTS: treatment costs were $24,605 MXP, $18,505 MXP and 17,380 MXP for meropenem, imipenem and ertapenem respectively.  Ertapenem savings range from $7,225 for meropenem to 1,125 MXP for imipenem. Results from scenarios with increased risk for P. aeruginosa infection at year 2 and 3 resulted in cost of $26,221 and $27,836 MXP for meropenem respectively, $20,121 MXP and $21,736 MXP for imipenem and $17,380 MXP for ertapenem in both years.  Mortality rate increase from 3.6% to 5.4% in the meropenem and imipenem groups and stay steady for ertapenem. CONCLUSIONS: ertapenem is a cost-effective and cost-saving alternative for treating enterobacteria producing beta-lactamases of extended spectrum (BLEES) sepsis in the Mexico Children's Hospital “Federico Gomez”.