The present invention relates to a method for determining a lateral relative movement between a processing head and a workpiece during processing the workpiece as well as a device to carry it out. In the method a surface of the workpiece (12) is illuminated in the region of the processing head with an optical radiation (2). The optical radiation (3) reflected from the surface of the workpiece (12) in the region of the processing head is repeatedly detected in a locally resolved manner by an optical detector (9), which is firmly fixed mechanically to the processing head, to obtain optical reflection patterns. The repeated detection occurs in temporal intervals in which the temporally successive reflection patterns of overlapping surface regions of the workpiece (12) are obtained. The lateral relative movement is determined by comparing the temporally successive reflection patterns. The method and the corresponding device permit contactless measurement of the relative movement between the processing head and the workpiece with great precision.