To obtain homogeneous distribution of the dose over extended fields in radiotherapy of Hodgkin''s disease, for an exact dosage within the irradiated region it is necessary to consider the topography of the patient. The skin protective build-up effect due to the use of bolus materials would be lost with telecobalt irradiation, and tissue compensating filters with a large surface are to be preferred. A simple method of making such filters by Moire topography is described. The way to obtain a compensation filter for extended areas is demonstrated by an example showing how to construct it from Pb plates correct in scale and layerwise.