Objective: The Mini-CEX, which is an evaluation method of clinical skills, was used in a medical residency program for assessing its results over time and to determine its validity and reliability. Materials and methods: The evaluation system was standardised with three the Mini-CEX being applied over one year to first-year medical residents of internal medicine and sub-specialties in the Faculty of Medicine of Universidad Peruana Cayetano Heredia, Lima, Perú. Differences between the three evaluations were measured using the Kruskal-Wallis test. The degree of reliability was measured using the Cronbach alpha test, and construct validity with factor analysis. Twenty teachers were trained. Each one of fourteen residents was evaluated three times. Results: The observations lasted 46.5 ± 26.1 minutes and feedback 20.1 ± 11.1 minutes. The factor analysis found one dimension. The overall Cronbach alpha score was 0.92. A significant improvement was observed in the residents in Physical Examination, from 6 (5.8-7.0) to 7.5 (6.8-8.0) p=. 028, clinical judgment, from 6 (6.0-7.2) to 8 (7.0-8.2) p=.021, and overall rating, from 7 (6, 0-7.6) to 8 (7-8) p=. 043. The satisfaction levels of residents and teachers with the method were 8/9 and 9/9, respectively. Conclusion: The test was well accepted by residents and teachers, and as it had a high level of reliability and construct validity, its use is recommended in medical residency programs.