ABSTRACT: In this paper we propose a mathematical programming model to optimize the tactical planning of the surgery service of a complex Colombian Hospital by using efficiently its resources, seeking for greater financial incomes and analyzing its capacity. In the model, we consider the main resources involved before, during and after surgical procedures. The main results are: a) the post-operatory beds, especially in the intensive care unit (ICU) and at the surgical ward, are the limiting resource of the capacity of this service; b) There is an average underutilization of 48.4% in operating rooms and 33% in the available human resources (mainly surgeons and anesthesiologist); d) reducing the duration of the pre- and post-surgery stay is an option to increase the availability of beds. Key findings suggest the following improvement options: a) Closing or disabling some operating rooms, could reduce the costs and improve the utilization of the service without jeopardizing the fulfilment of its demand; b) working on the increase of the demand for outpatient surgeries could be a good option, since they do not require additional beds; c) combining the closure of operating rooms and the increase of demand for outpatient surgery is an interesting option.