Production planning and scheduling for sawmills poses many challenges. The solution approaches most commonly used to tackle this problem in the forest industry are: simulation, mathematical programming models, and a combination of both. In this paper we compare the results of using a mathematical model versus a heuristic in scheduling and production planning of a sawmill. We developed a mathematical model that takes into account most of the complexities involved in scheduling and production planning of a sawmill, for a one-month planning horizon. One of the main difficulties is that the supply of hardwood lumber pieces can have different diameters, which are not known in advanced. The cutting patterns that can be used depend on the diameter of the lumber piece to be cut. The cutting pattern, on the other hand, determines the products that are produced. Sometimes suboptimal cutting patterns must be used in order to meet the production plan. We compare the quality of the solutions generated by the mathematical model and the heuristic. Several experiments were conducted using data that represents situations faced by a Chilean sawmill.