This nationwide follow-up study concerns the pattern of malignant tumours in a cohort of patients with psoriasis, at an average of 9.3 years after discharge from hospital. The study confirms that the significantly increased risk of cancer in these patients, amounting to 1.4 times that in the general population, is mainly due to cancer of the skin and lung in both sexes and cancer of the pharynx and larynx in men. Non-melanoma skin cancer is the most common malignancy, occurring in 196 of 795 patients with cancer: standardized incidence ratio (SIR, the ratio of observed to expected cancers) 2.4 for men and 2.6 for women. This means an overall lifetime risk (up to the age of 75 years) of 14.1%. In particular, squamous cell carcinoma (SCC) by itself (n = 45, SIR 3.9 for men and 4.7 for women), cancer in multiple sites (SIR 5.9 for basal cell carcinoma (BCC) and 11.7 for (SCC) and SCC on the lower extremities (SIR 18.0) are frequent. Women run the highest risk of BCC in the age range 20-40 years, while men in the age range 30-60 years run a particularly high risk of SCC. When monitoring patients extensively treated for psoriasis, this aberrant pattern of cancer should be taken into account.