The paper reports on a study carried out to detect airgap eccentricity in large 3-phase induction motors. The philosophy of using a unified online monitoring strategy is presented and the reasons for selecting line current and frame vibration as the monitored parameters are discussed. A theoretical analysis is presented which predicts the presence of unique signature patterns in the current and vibration spectra which are only characteristic of eccentricity. The theoretical predictions are verified by experimental results from a special fault producing test rig and on-site tests in a power station.