The Surgery Department generates a sizeable amount of the income of a hospital. This study evaluates the variability in the scheduling of surgeries and how this threatens the efficiency of the service. This study uses an algorithm for the generation of two schedules that were later compared with a manually-generated schedule in a hospital in Colombia. The difference between the generated schedules is the inclusion or lack thereof of the maximum time deviations in surgery times, under the assumption that these are caused by external factors and may be eliminated. Results show that by using an automatic algorithm to schedule the surgeries response time and operating room use can be improved. Moreover, it can be concluded that the variability associated with manual scheduling has a greater impact than the one associated to other factors in the service performance indicators.Keywords: