The most common etiological agents in periprosthetic infections are Escherichia coli and Staphylococcus aureus. The frequency of these infections are found in knee replacement with 0.68 to 1.60% compared to the hip with 0.67 to 2.4%. To identify what are the most common etiologic agents in periprosthetic infections in elderly patients with primary hip and knee surgery. An observational study, transverse and retrospective case series was performed in a period from June 2011 to December 2014, patients over 60 years with a diagnosis of periprosthetic infection by two positive cultures with antibiograma. 62 patients were evaluated 59.7% were infections of knee and hip 40.3%, 59% were infections by Escherichia coli and Staphylococcus aureus 22%. The best sensitivity reported antibiotic trimethoprim-sulfamethoxazole was 40.3%. The largest penicillin G resistance 32.2%. The most common causative agents were Escherichia coli and Staphylococcus aureus.