This paper presents a stress and fatigue life analysis for the shaft of a 100 hydro-generator. Normal and shear stresses were measured at the cylindrical section of the shaft at several power levels. A finite element model was developed to find points with stress concentration and the corresponding stress concentration factor. Analytical models taken from the literature were implemented to calculate stresses during phase-to-ground and phase-to-phase failure. Stresses were linked with the generation history of the machine taken each hour during one year to obtain the stress history. With the stress history, the Wang-Brown multiaxial fatigue model and the Miner’s rule were used to estimate the fatigue life.
 Stresses on the shaft were found to be dependent on the generated power. Operation at partial load (between 30 and 60% of full load) was found to produce higher vibration in comparison with operation at power greater than 60% of full load. Changing the power level produced higher damage than the vibration produced during operation at a steady state condition. It was found that the shaft has a practically infinite life even when the damage produced during electrical failure was considered.