Photochemotherapy with psoralens + ultraviolet (UV)-A light (PUVA) has been used for about 16 years to treat psoriasis. Some reports have indicated a higher frequency of cutaneous squamous cell carcinoma among treated patients. The results are not consistent, however, and are not generally conceded. The material from Ullevaal Hospital comprises 585 patients who have been treated with PUVA from 1977 to 1991. Three patients developed cutaneous squamous cell carcinoma, but in one of them the tumour developed before start of PUVA treatment. The two others had received only very small doses. One of them had an intraepithelial cancer of the penis. In addition the authors registered various internal cancers in 25 patients. The Norwegian Cancer Registry compared the patient material with a matched control group as regards sex, age and age-specific incidence rate. There was no statistically significant difference in incidence between the patient and the control group. 15 refs., 1 tab.