Machine tools cannot produce accurate parts if performance degradation due to wear in their subsystems (e.g., spindle units) is not identified and con-trolled. Appropriate maintenance actions delay possible deterioration and mini-mize machining system stoppage time that leads to lower productivity and higher production cost. Measuring and monitoring machine tool condition has become increasingly important because of the introduction of agile production and in-creased requirements for product accuracy. Condition Based Maintenance (CBM) techniques, such as vibration monitoring, are becoming a very attractive method for companies operating high-value machines and components. One of the most common problems of rotating equipment, such as machine tool spindle units, is the condition of bearings. Vibration analysis can diagnose bearing damage by measuring the overall vibration of a spindle or, more precisely, by high-frequency techniques such as enveloping. This paper focuses on the use of vibration analysis to monitor and analyse the condition of machine tool spindle units. The method is a case study at a manufacturing company in Sweden. CBM, using vibration moni-toring, is implemented on different types of machine tools. The results of the im-plementation, as well as a vibration analysis of a spindle unit and its cost effec-tiveness, are presented in the paper.