A method for detecting an accretion of ice on a rotor blade of a rotor of a wind turbine, wherein the rotor can be operated at a variable rotational speed, comprising the steps: - recording a wind speed of a wind acting upon the rotor, - recording an operating variable that is dependent on the wind speed, - comparing the recorded operating variable or the recorded wind speed with a reference variable of a characteristic wind-speed-dependent operating-variable curve of the wind turbine, wherein the characteristic operating-variable curve indicates an operating variable assumed to be optimal in dependence on the wind speed, - detecting an accretion of ice on the rotor blade if the recorded operating variable, or the recorded wind speed, deviates from the reference variable by at least a predetermined minimum deviation, wherein - the minimum deviation is specified in dependence on the wind speed, wherein - for wind speeds below a rated wind speed (V N), an output power, generated by the wind turbine from the wind is recorded as an operating variable, - for wind speeds above a rated wind speed (V N), a blade angle set to limit the output power is recorded as an operating variable, and - an accretion of ice is detected if - the recorded output power (P R) deviates from the reference power by at least a predetermined minimum-deviation power, and/or - the recorded blade angle deviates from the reference angle by at least a predetermined minimum-deviation angle, and/or - the recorded wind speed deviates by a predetermined minimum-deviation speed from a wind speed assigned to the recorded output power or from a wind speed assigned to the recorded blade angle, characterized in that the minimum-deviation power, the minimum-deviation angle or the minimum-deviation speed is in each case specified in dependence on the wind speed. - recording a wind speed of a wind acting upon the rotor, - recording an operating variable that is dependent on the wind speed, - comparing the recorded operating variable or the recorded wind speed with a reference variable of a characteristic wind-speed-dependent operating-variable curve of the wind turbine, wherein the characteristic operating-variable curve indicates an operating variable assumed to be optimal in dependence on the wind speed, - detecting an accretion of ice on the rotor blade if the recorded operating variable, or the recorded wind speed, deviates from the reference variable by at least a predetermined minimum deviation, wherein - the minimum deviation is specified in dependence on the wind speed, wherein - for wind speeds below a rated wind speed (V N), an output power, generated by the wind turbine from the wind is recorded as an operating variable, - for wind speeds above a rated wind speed (V N), a blade angle set to limit the output power is recorded as an operating variable, and - an accretion of ice is detected if - the recorded output power (P R) deviates from the reference power by at least a predetermined minimum-deviation power, and/or - the recorded blade angle deviates from the reference angle by at least a predetermined minimum-deviation angle, and/or - the recorded wind speed deviates by a predetermined minimum-deviation speed from a wind speed assigned to the recorded output power or from a wind speed assigned to the recorded blade angle, characterized in that the minimum-deviation power, the minimum-deviation angle or the minimum-deviation speed is in each case specified in dependence on the wind speed. - an accretion of ice is detected if - the recorded output power (P R) deviates from the reference power by at least a predetermined minimum-deviation power, and/or - the recorded blade angle deviates from the reference angle by at least a predetermined minimum-deviation angle, and/or - the recorded wind speed deviates by a predetermined minimum-deviation speed from a wind speed assigned to the recorded output power or from a wind speed assigned to the recorded blade angle, characterized in that the minimum-deviation power, the minimum-deviation angle or the minimum-deviation speed is in each case specified in dependence on the wind speed. - the recorded output power (P R) deviates from the reference power by at least a predetermined minimum-deviation power, and/or - the recorded blade angle deviates from the reference angle by at least a predetermined minimum-deviation angle, and/or - the recorded wind speed deviates by a predetermined minimum-deviation speed from a wind speed assigned to the recorded output power or from a wind speed assigned to the recorded blade angle, characterized in that the minimum-deviation power, the minimum-deviation angle or the minimum-deviation speed is in each case specified in dependence on the wind speed.