6-Thioguanine has been highly effective in treating and maintaining improvement in patients with psoriasis. A study comparing efficacies with methotrexate would be extremely useful. Because of the possibility of severe bone marrow depression, 6-thioguanine is not a first-line treatment. However, with new dosing regimens, proper laboratory monitoring, and further studies, use of 6-Thioguanine could expand in the future.