The research described was performed with diagnostic tools used to detect damage to dynamic mechanical components in a wind turbine gearbox. Different monitoring technologies were evaluated by collecting vibration and oil-debris data from tests performed on both a ‘healthy’ gearbox and a damaged gearbox that were mounted on a dynamometer test stand at the National Renewable Energy Laboratory (NREL). The damaged gearbox tested had been removed from the field after it experienced component damage because of two events that resulted in the loss of oil. The gearbox was re-tested under controlled conditions by using the NREL dynamometer test stand. Preliminary results indicate that oil-debris and vibration data can be integrated to improve the assessment of the health of the wind turbine gearbox. Copyright © 2012 John Wiley & Sons, Ltd.