In this paper the radial and axial vibrations of a rigid shaft supported by a pair of angular contact ball-bearings is studied. The effect of ball size variation in the bearings on the vibration of the shaft is investigated. A computer program was developed to simulate this effect, with the results presented in time and frequency domains. All results show that off-sized balls in the bearing cause vibrations at cage speed and its harmonics, depending on their arrangement within the bearing. Symmetric combinations will produce vibrations at the multiples of the cage speed and all other combinations will produce vibrations at the cage speed. The highest radial vibrations due to ball size variation are at a speed of half of the number of balls times the cage speed.