The association of cancer and Crohn's disease is well documented and c
omprises 2 % of cases, but the onset of a malignant lymphoma during th
e course of the disease is a very rare finding (20 cases reported). A
patient presented with a malignant plasmocytic lymphoma complicating a
n ileal Crohn's affection. Both clinical and radiological diagnosis we
re uncertain, most such cases being discovered perioperatively, confir
mation of the diagnosis being provided by histology and immunohistolog
y, which also allow classification of the lymphoma to allow adaptation
of complementary postoperative treatment.