Cyclophosphamide (CPA) is an alkylating agent widely used as an immunosuppressive agent in the treatment of several autoimmune diseases, including systemic lupus erythematosus. Its teratogenic effect has been well studied in different experimental mammalian and non-mammalian animal models. In humans, 11 cases of CPA teratogenesis have been documented.We present a case of a patient with Klippel-Feil syndrome inadvertently exposed to CPA and prednisone in utero during the first trimester. CONCLUSIONS This case of possible cyclophosphamide embryopathy provides evidence of teratogenesis as an etiologic agent in developmental field defects such as Klippel-Feil syndrome.Copyright © 2012 Wiley Periodicals, Inc.