Objective: In jawbones, ameloblastomas and odontogenic keratocysts share many clinical features in common such as aggressiveness, high recurrence rates and radical management options. Understanding the pathogenesis and biological aspects of these tumors would improve the success of diagnose and treatment procedures. The aim of this study was to exhibit the reasons of high recurrence rates and growth potentials of ameloblastomas and keratocystic odontogenic tumours by investigating the expression of IL-1? and IL-6 and IL-1? -889 gene polymorphism. IL-1? and IL-6 are shown as very effective tissue degrading factors in bone remodelling. Study Design: This study included 25 cases of ameloblastomas, 41 cases of keratocystic odontogenic tumors (parakeratinized odontogenic keratocysts) and 8 cases of orthokeratinized odontogenic keratocysts. All histological slides were stained immunohistochemically to show the expression of IL-1? and IL-6. Restriction fragment length analysis was used to investigate the cytokine gene polymorphism. Results and Conclusions: The higher expression rates of IL-1? and IL-6 were associated with tumor size in ameloblastomas and with cyst wall thickness in keratocystic odontogenic tumors. This finding suggested us that the cytokines IL-1? and IL-6 play a role on aggressive behaviour of ameloblastomas and keratocystic odontogenic tumors by making easy bone resorption. In addition, IL-1? (-889) T polymorphism was found consistent with increased IL-1? expression but not seem as a risk factor on the development of these tumors. © Medicina Oral S. L.