The ankle is one of the most resisting to arthritis joints of the body, and the development of degenerative changes in it, always due to a pathologic condition or trauma. The aim of this study is to demonstrate the late post- operative results and the development of post-traumatic osteoarthritis in a series of 144 patients with malleolar fractures who have been operated with the principles and methods of AO. To judge our results, we used subjective, objective and X-Ray criteria. The main follow up was 8,6 years, final results were excellent and good in 74,3%, satisfactory in 14,6 and poor in 11,1% while post-traumatic osteoarthritis developed in 22.2% of the cases. The installation of post-traumatic osteoarthritis in malleolar fractures seems to be influenced by factors like age, sex, severity of fracture, quality of reduction and existence of posterior bone fragment bigger than 25% of the joint surface.