Measurement of maintenance performance is done on the basis of component history data in which service sojourns are distinguished according to whether they terminate in corrective or preventive maintenance. From the viewpoint of data analysis, corrective and preventive maintenance constitute competing failure modes. This article examines ways to assess maintenance performance without introducing statistical assumptions, then introduces a plausible statistical model for describing the interaction of preventive and corrective maintenance, and finally illustrates these with examples from the Nordic TUD data system. (C) 1997 Elsevier Science Limited.