Background. Antimicrobial resistance (AMR) is a global threat to public health. Antibiotic stewardship programs (AMSP) promote the proper use of antimicrobials, improve clinical and economic outcomes, and helps containing the AMR. Aim: To evaluate the diagnostic phase of the AMS programs and early implementation of AMS at three high complexity hospitals that belong to the social security system in Peru. Methods: A quasi-experimental multicenter study was implemented. The construction of the AMSP, microbiological baselines, antimicrobial consumption and consensus on AMS activities were evaluated at the diagnosis and early implementation periods of the AMSP. Results: Following implementation, hospitals doubled their score of resources and processes available for the AMS program from 6.75 to 13.75. The prevalence of extended spectrum beta-lactamase producing enterobacteria was 50-60% while Pseudomonas aeruginosa averaged 69% resistance to carbapenems. The defined daily dose (DDD) of ceftriaxone was 13.63, vancomycin 7.35 and meropenem 6.73 in average. Hospitals A and C decreased the use of antimicrobials (30-50%). Discussion: The implementation of the AMSP in the three hospitals was achieved through diverse strategies designed by multidisciplinary teams, which in addition to its articulation, reduce the consumption of broad spectrum antimicrobials at an early stage.