A knowledge of the intimate relationships between the transverse colon, transverse mesocolon and duodenum is often of critical importance in the roentgen analysis of upper abdominal pathology. Detailed study of their anatomic relationships was made by sections derived from frozen cadavers.These observations are essential in the roentgenologic interpretation of a variety of disease states including defect of the mesocolon with internal herniation into the lesser sac, masses developing within the mesocolic leaves, secondary effects on the descending duodenum from carcinoma of the hepatic flexure, extension of neoplasms of the duodenum to involve the colon, acute pancreatitis, abdominal aneurysm, and distinction of an abscess of Morison’s pouch from an inframesocolic abscess.Diagnosis of spread from colonic carcinoma by the effect of lymph node metastases upon the duodenojejunal junction is shown.