Background: Resistance by extended-spectrum beta-lactamase (ESBL) is the most common antimicrobial resistance and of public health importance. Objectives: To describe ESBL producing bacteria characteristics in a national reference hospital. Design: Cross sectional, descriptive study. Setting: Hospital Nacional Daniel Alcides Carrión, Callao, Peru. Materials: Records of secretion cultures done in the hospital Laboratory of Microbiology during 2012. Methods: Patient data (age, sex and service from which the sample was received) and sample data (date of collection, sample type, microorganism found, sensitivity and detailed classification as ESBLproducing bacteria) were analyzed. Main outcome measures: Characteristics of infections by ESBL-producing bacterias. Results: Study included 3 149 samples, 70.9% (2 235) from female patients; 29.4% were cultures positive for ESBL-producing bacteria....