The empirical treatment of urinary infections is complicated by the presence of multiresistance and resistance to extended-spectrum beta-lactamases (ESBLs). The objective of this study was to describe the patterns of antibiotic resistance of Escherichia coli strains isolated from urine cultures and the clinical-epidemiological factors associated with the presence of ESBLs in a pediatric and an adult group. A total of 353 strains were collected from the Emergency and Hospitalization Sector of the Cayetano Heredia Hospital over 14 months, and 45.9% of the isolated strains were multiresistant. The rate of resistance to ESBLs in the pediatric and adult population was 16.3% and 31.1%, respectively, and 63.6% of the resistant strains were isolated from outpatients. The presence of ESBLs was associated with hospitalization in pediatrics, use of diapers, and the presence of neurogenic bladder in adults. These factors should be considered in selection of an antibiotic treatment. Moreover, epidemiological reporting programs and models should be implemented for reduction of risk factors.