Roadheader, one of the mechanized excavation equipments, has an exceptional place among the other excavation methods. Determination of the stability states of the roadheader is an important matter for the efficiency of excavation. For this reason, a new method has been developed to obtain numerical values that indicate stability states of such machines. The method has been developed for both longitudinal and transverse cutting head type machines by establishing stability equations for states of turning around the vertical axis, turning to the side direction, turning to the back direction and sliding in all cutting modes. A computer program based on these equations has been written in C++ programming language. The stability analysis can be made either for one point on the excavation face or whole face. Obtained values can be used to compare the stability states of various roadheaders in the same cutting condition as well as using to compare the stability states of a roadheader. A stability index that has also been established can only be used to compare a stability state of a roadheader in different cutting conditions. The developed methodology was tested in a transverse cutting head type roadheader for arcing, lowering and lifting modes. It has been obtained that the stability state of turning around the vertical axis of the roadheader is the most critical state especially in arcing mode. The effects of the machine design parameters, cutting head and tunnel parameters on the stability of the roadheaders can also be investigated by this method. (c) 2005 Elsevier Ltd. All rights reserved.