The case of a patient with primary mesenteric venous thrombosis presenting with massive dilatation of almost the entire colon is described. The differential diagnosis suggested by this presentation is briefly discussed with special attention to the diagnosis of acute colonic pseudoobstruction. Possible reasons for the atypical presentation of acute mesenteric venous thrombosis should, therefore, be considered in the differential diagnosis of all patients presenting with colonic distention and pseudoobstruction.