We report on a 60-year-old man who presented as an emergency with an acute abdomen in 2003. He had been completely well until shortly before this presentation with no symptoms of note; specifically, he described no weight loss, no night sweats, no fevers, and no change in bowel habit. Apart from the obvious acute abdomen, clinical examination was unremarkable. There was no peripheral lymphadenopathy and no hepatomegaly, and it was noted that the man had previously had a splenectomy. At presentation, routine blood analysis was normal apart from a lymphocytosis of 19.8 ϫ 10 9 /L. The patient underwent an emergency laparotomy. During the operation, he was found to have a perforated duodenum and several large periduodenal lymph nodes. These were biopsied, and he underwent a gastrojejunostomy. The duodenum had perforated through a macroscopic tumor.The resected duodenum and lymph node biopsy obtained during the operation showed a nodular infiltrate of small lymphoid cells with irregular nuclei and inconspicuous cytoplasm, interspersed with histiocytes with copious cytoplasm. The cells were strongly CD20 ϩ , CD3 Ϫ , and CD5 ϩ and demonstrated nuclear expression of Cyclin D1 protein. Flow cytometric analysis of the circulating lymphocytes revealed a clonal population of B cells that were positive for CD19, CD5, CD23, CD79b, and FMC7 and were strongly positive for Lambda surface immunoglobulin. This was all consistent with a diagnosis of mantle-cell lymphoma (MCL). Fluorescent in situ hybridization (FISH) analysis using an IGH/CCND1 dual-color fusion probe set from Abbott Laboratories (Abbott Park, IL) demonstrated a t(11; 14)(q13:q32) translocation. Staging computed tomography revealed widespread lymphadenopathy, including in the mediastinal, retrocrural, and para-aortic regions, with subhepatic soft tissue masses of up to 3.5 cm. His bone marrow was heavily infiltrated with disease.After recovery from the operation, the patient was treated within a United Kingdom national MCL trial and entered complete remission. Treatment was with oral fludarabine and cyclophosphamide. Four years later, he developed acute myeloid leukemia while still in complete remission of lymphoma and unfortunately died as a result.Review of his notes shows that, in 1993, 10 years before diagnosis, the patient had been admitted to the hospital with an episode of severe abdominal pain. In addition, he had recently lost weight but had no other symptoms. His full blood count revealed a mild thrombocytopenia (78 ϫ 10 9 /L) with normal hemoglobin (15.9 g/dL) and lymphocyte counts (1.32 ϫ