We have studied DNA repair in patients with psoriasis aiming at investigating the importance of repair in chemically induced cancer. An increased risk of non-melanoma skin cancer has been observed in psoriasis patients extensively treated with tar, methotrexate and photochemotherapy (psoralen + UVA). We measured the DNA repair capacity (DRC) by a host cell reactivation (HCR) assay in lymphocytes from psoriasis patients with and without basal cell cancer and non-psoriatic persons with and without basal cell cancer (4 x 20 study persons). Among psoriasis patients we observed a significant lower DRC in patients with skin cancer compared to patients without skin cancer (P = 0.015; Mann-Whitney, one-sided). Using the median of the healthy control group (group 4) as a cutoff value to divide the psoriasis patients into groups of high and low repair, we found that individuals who had a low repair capacity had a 6.4-fold increased skin cancer risk compared to individuals with high repair (95% confidence interval (CI), 1.44-28.5). The level of DNA repair was correlated with the age at which the psoriasis patients got their first skin cancer. The lower the level of DNA repair, the earlier the psoriasis patients had their first skin tumor (P = 0.070 Spearman; one-sided). Psoriasis patients without BCC had marginally higher repair than healthy controls (P = 0.11, Mann-Whitney, two-sided). We found no difference between BCC patients without psoriasis and healthy controls. In conclusion, these findings suggest a protective role of DNA repair in a predominantly chemically induced cancer.