Pancreatic ectasia (PE) is a common incidental finding in people dying from uremia. It has been described as dilatation of acini, inspissation of secretions, and proliferation of ductal cells. PE occurred in 17 macaques, 11 of which were known to have been uremic. The lesion was studied by light and electronmicroscopy and histochemistry and by construction of a three-dimensional model of a dilated acinar ductal system from serial semithick Epon sections. Atrophic acinar cells interspersed with clumps of centroacinar cells lined all portions of the system. There was no evidence of ductular proliferation. Fibrillar material was present in the dilated acinar lumens and associated with epithelial cells and leukocytes, but no blockage of the system was demonstrated. The lesion is similar to those induced by a variety of experimental procedures and to the pancreatic lesions of cystic fibrosis.