The invention relates to a method and a device for determining the position of defects or damage on rotor blades (4) of a wind turbine (1) in an installed state, comprising the steps: a. a localisation instrument (5) is guided along the rotor blade (4) and the defect or damage is detected; b. the localisation instrument (5) has a GPS module (6) by means of which the GPS data of the localisation instrument (5) is detected at the defect or damage; c. the position of the investigated wind turbine (1) is detected by means of the GPS module (6); d. using the position data of the wind turbine (1), the hub height (n) of the wind turbine (1) is retrieved from a database and the distance (d) of the defect or damage of the rotor blade (4) from the hub (34) is calculated in an evaluation unit (8) from the difference between the GPS data of the localisation instrument (5) and the hub height (n) of the wind turbine and in accordance with the rotor blade position.