A method and a device for dynamic measurement of the radial deformation of a bearing ring (12) of a rolling bearing (10) for a rotating element (16), a glass fiber segment (22) of a fiber optic sensor (24) that is fixed in or to the periphery of the bearing ring, a light signal which has been generated by the light source (30) being injected into the glass fiber segment, and the light signal passing through the glass fiber segment being detected by a detector (34), the longitudinal deformation of the glass fiber segment being determined from the change of at least one parameter of the light signal, when the light signal passes through the glass fiber segment, in order to determine the corresponding radial deformation of the bearing ring.