To provide a method and a device by which the three-dimensional variation of the eccentricity of a hollow block along the ordinate of the hollow block is detected and especially the degree of the eccentricity which is actually properly useable is indicated.

This method is for deciding the eccentricity of the hollow block with at least one measuring device with which the wall thickness s of the hollow block in the vertical position and the circumferential position of the hollow block 1 before, when or after the hollow block 1 which is advanced side by side in the direction of the longitudinal axis L is passed through a rolling mill. A measuring device 2 is moved in the direction of the longitudinal axis L and/or the circumferential direction of the hollow block 1 during measurement and the measurement of the wall thickness is carried out several times during this motion in this case. This device is for carrying out the above method.