To the Editor.— Recently two important papers appeared dealing with the development of malignancy during methotrexate treatment for psoriasis.1,2 At the 9th Scandinavian Congress of Dermatology in Oslo, Norway, June 10, 1971, we had the opportunity of presenting a paper in which three cases were discussed, in whom carcinoma appeared during long-time treatment with methotrexate, in two cases renal carcinoma and in one case mammary carcinoma. In all three cases the skin disease was very severe psoriasis, and they had received cytostatics during more than two years before the diagnosis of the carcinoma (Figure). In these three cases it is not possible to postulate the treatment being the cause of the malignant tumors. It is not, however, excluded that the treatment with methotrexate may have hastened the death of the patients. During a short time five cases are now reported in whom development of carcinoma had occurred during