The vibration properties of ball bearings supporting mechanical systems such as small coupled high speed turbo alternators or machine tool spindles and their cutting tools, can have an important influence on their performance. Even if the bearings are geometrically perfect, they can still be a source of untoward vibrations in a dynamical system. Clearly, these vibrations are also a contributary factor in the life of the bearings themselves and hence, indirectly, of the complete system. This paper discusses the dynamical behaviour of a simple model comprising a uniform rotor supported by two angular contact ball bearings. The significance of certain vibrations associated with these bearings is discussed, firstly when they are geometrically perfect and then when the bearing rings are misaligned.