Rough set theory, which emerged about 20 years ago, is nowadays a rapidly developing branch of artificial intelligence and soft computing. We will use rough set theory for modeling a classification system and applying genetic operations to a population of trees, which will be induced randomly or via the C4.5 method from the decision table with different pruning-constant settings. At first glance, the methodologies we discuss, namely, rough set theory and genetic programming, have nothing in common. However, it is interesting to try to incorporate these approaches into the hybrid system. The challenge is to get as much as possible from this association.