The objective of this study was to investigate the prolonged complications of untreated diabetes on histomorphology of rabbits. Diabetes mellitus was experimentally induced in one group of New Zealand white male rabbits by intraperitoneal administration of four doses of alloxan @ 80 mg/kg b.w. at weekly intervals following 12 h fasting. Other group of rabbits served as healthy controls that received isotonic saline in a similar manner. The establishment of diabetes mellitus was confirmed by fasting blood glucose levels. For histomorphological study of different organs, 50% of the animals were killed after 7 weeks and the rest after 26 weeks. Routine haematoxylin and eosin stain and Gomori’s modified stain were used. The blood glucose level of diabetic rabbits increased significantly throughout the experimental period. The peak values for blood sugar were on the sixth week of the study. Further, histomorphological alterations were recorded in pancreas, kidneys, lungs, heart and brain in diabetic rabbits. However, mild changes were observed in gastrointestinal tract with proliferation of yeasts in the stomach. With the progress of untreated diabetes, the histoanatomical alterations intensify and extend to almost all organs of the body and appear to increase the susceptibility of gastric mucosa to yeast cell proliferation.