Due to cyclic loading conditions, cracks frequently appear in rotating machines. The propagation of fatigue cracks in shafts can provoke severe accidents with high risks of people. During the rotation of the cracked shaft, the crack opens and closes in what is called the breathing mechanism, and consequently the behavior of the shaft becomes nonlinear. In the present paper, the propagation of a semi-elliptical crack contained in a rotating shaft has been analyzed considering the nonlinear effect of the crack as the shaft rotates. To this end, an integration algorithm which allows obtaining the crack front evolution has been improved. This procedure uses the Paris-Erdogan Law to determine the advance at a few points along the crack front and uses the general expression proposed previously by the authors that gives the Stress Intensity Factor along the crack front of an elliptical crack in a rotating shaft in terms of the crack depth ratio, the crack aspect ratio, the relative position on the front and the angle of rotation. Several initial semi-elliptical surface crack geometries have been analyzed. For each geometry, the evolution of the crack front has been studied, analyzing the variation of the crack aspect ratio against the crack depth ratio. By the moment, no fatigue growth analyses of surface cracks in rotating shafts, taking into account the breathing mechanism and considering the nonlinear behavior of the shaft, have been found in the literature.