Commissioning is gaining increasing recognition as a cost-effective strategy for reducing commercial building energy use. Although the success and cost-effectiveness of commissioning projects depends on how well the benefits of commissioning persist over time, this aspect of commissioning is not well understood. The persistence of commissioning benefits was recently studied in a PIER project evaluating ten buildings that were commissioned at building start-up at least two years ago. The researchers examined the commissioning reports, control algorithms, EMCS point measurements, and energy use data, and conducted operator and commissioning provider interviews to investigate the persistence of commissioning benefits. In addition, they conducted site visits in a sample of the buildings. A set of commissioning measures was selected for each building to compare the persistence of benefits. Persistence was measured both qualitatively through a discussion of occupant comfort and decreased maintenance and quantitatively through estimations of energy savings. This paper reports the results of the study. The discussion includes how well the benefits of commissioning persisted over time, reasons for declining performance, and methods for improving persistence. The results provide valuable insight into how to estimate the persistence of commissioning information central to the cost benefit analyses routinely performed for commissioning measures.