The frequency of malignant neoplasms was studied in 248 psoriatics treated with a single, weekly, oral dose of methotrexate ranging from 5 to 25 mg. The follow-up period ranged from 5 to 14 years with a median of 7 years. The following 10 malignant neoplasms were found: ovarian cancer 3, breast cancer 2, esophageal cancer in 1 male, pancreatic cancer in 1 female, malignant lymphoma in 1 female and 1 male and 1 squamous cell carcinoma of the scrotal skin. As the observed number of malignant neoplasms was considerably smaller than the expected number, it is concluded that methotrexate therapy as used in the treatment of psoriasis does not seem to contribute to the development of malignant neoplasms.