Psoriasis may lead to subsequent colorectal cancer, since chronic systemic inflammation is the common etiologic factor in both psoriasis and colorectal cancer. It is a matter of dispute whether biological agents used in the treatment of psoriasis cause predisposition to colorectal cancer as a result of their immunosuppressive effect. Medical records of psoriasis patients who underwent colonoscopy before biological agents were reviewed. Colonoscopy was performed in all patients who were aged 50 years and older and in patients younger than 50, if they had positive fecal occult blood test results. The study included 95 patients between the age of 34 to 84. Colonoscopy results revealed tubular adenoma in 16 (16.8%) patients, hyperplastic polyps in 7 (7.4%) patients, villous adenoma in 1 (1.1%) patient, and tubulovillous adenoma in 1 (1.1%) patient. Two patients were diagnosed with colon cancer detected by a former colonoscopy, which was recommended by their dermatologist before the biological agent treatment plan. These results revealed that adenomatous polyps which can evolve to colon adenocarcinoma were the most frequent polyp type in patients with psoriasis. We suggest that routine colonoscopy should be performed before the initiation of biological therapy in psoriasis patients who are aged 50 years old and over.