The focus of this case study and cost–benefit analysis is an application of a condition-based monitoring (CBM) tool installed in a 700kW wind turbine generator at a project based in the USA. The installation was in response to reports that several wind farms had experienced catastrophic gearbox failures, resulting in exorbitant costs and lost revenues. It began in summer 2003 with a cooperative pilot study, the objective being implementation of a ‘trial installation’ that would demonstrate the benefits of a CBM system on a wind turbine to help prevent catastrophic failures.