Dihydropyrimidine dehydrogenase (DPD) deficiency has been identified as the cause of rare severe life threatening reactions to fluoropyrimidines. The first case was reported by Tuchman et al in a 27 year old woman who had undergone adjuvant chemotherapy with cyclophosphamide, methotrexate, and 5-fluoruracil and developed severe neurological complications. Diasio et al reported the second case again in a women being treated with 5-fluoruracil for breast cancer.