While there are several manuscripts describing the articular surfaces of the ankle joint and the fibula itself, there is no study describing the outer surface and the degree of curvature of the fibular malleolus. This paper aims to approximate the sagital curvature of the outer surface of the lateral malleolus mathematically. Such data would facilitate the design of the anatomic plate that can be used for the ostheosynthesis of the fibular malleolus fracture. 30 males who were examined in the emergency department due to ankle sprains, where they underwent a standard anteroposterior x-ray of the ankle in the neutral position were recruited. The radiographs which revealed no bony injury were digitized and statistically processed. A mathematical function for each separate fibula was obtained through the processing of the digitized x-rays. When all the functions were applied to one graph, common traits of all fibulas were noted. The mean value of all functions was obtained and it corresponds to the polynomial function of degree 6. Mathematical approximation of the curvature is a simple and reliable method that can be applied to other ellipsoid human bone structures besides the ankle, thus being a valuable method in anthropometric, radiological and virtual geometric calculations.