The histopathology of 145 malignant lymphomas of the small intestine in Iraq have been studied and results compared with the clinical and immunological findings. The most common pathology was an intense mucosal lymphoplasmacytic proliferation effacing the villi and crypts partially or completely. This was either 'pure', usually of mature plasma cells limited to the lamina propria or associated with a fullblown lymphoplasmacytic lymphoma, almost always of the upper small intestine. The syndrome presented as abdominal pain, chronic diarrhoea, clubbing and, sometimes, the serological demonstration of alpha heavy chains. Other types of lymphomas were associated with 'non-specific' mucosal inflammation or follicular lymphoid hyperplasia. They were either lymphocytic, plasmacytic or lymphoblastic with 'starry sky' histiocytic reaction, representing distinct clinicopathological entities unrelated to 'alpha heavy chain disease'. Hodgkin's disease was extremely rare in this series.