Objective. To investigate the aptitude degree of the critical reading in reports of clinical investigation in the residents of the different areas of medical specialties. Material and methods. It was elaborated and it validated an instrument to explore the critical reading in their abilities of to interpret and to judge. We studied 572 medical residents of eight units of the Mexican Institute of the Social Security: 292 of the medical area, 227 of the surgical area, 30 of the area of auxiliary in diagnosis and treatment, and 23 of the research area. Results. The median of the qualifications obtained, they were low (considering a theoretical qualification maxim of 100), for the residents of the three areas: medicine with 34, surgical whit 30 and auxiliary in diagnosis and treatment with 28.5. For the research area, the aptitude was a medium degree with 49. Of the 572 residents 98 (17.1%) it didn't surpass the limit of the accountable qualifications for a random effect. In the medical area we found a positive differential effect of the time of residence in the aptitude for the critical reading, particularly in the specialty of Internal Medicine. Conclusions. The development of the aptitude for the critical reading of reports of clinical investigation in general is low, the exception, are the residents in investigation and in certain measure those of internal medicine; in this last one it seems product of an intentional, grupal, systematic and progressive exercise
