Histopathological studies were made on 50 autopsied beagles to examine for spontaneous lesions and age changes. While many neonatal and juvenile dogs under one year died of pneumonia, aged dogs had various age changes in some organs. They were vacuolar and fatty degeneration, lipofuscin deposition, acidophilic crystalline intranuclear (ACN) inclusions and granulomatous aggregation of mononuclear cells in the liver; urinary casts, calcification, ACN inclusions, chronic interstitial nephritis and pyelonephritis in the kidney; fatty and vacuolar degeneration, and nodular hyperplasia in the adrenal gland; mucoepithelial cysts of the intestine; atrophy and cyst of follicles, and interfollicular cellularity in the thyroid gland. In addition, cystic hydronephrosis with pelvic dilatation in neonatal dogs, mild cerebral edema with ventricular dilatation, cyst of pituitary anterior lobes, lymphocytic thyroiditis, and dermatosis were noted. Tumorous lesions were observed only in a few aged dogs.