Dogs and cats that have been perfectly acceptable pets for many years may develop behavioral problems with old age. Most often these problems develop in animals that have never been very well behaved but have been tolerated by the owners until the problem has somehow exacerbated secondary to some other geriatric problem. The behavioral problems of old dogs most likely to be encountered by the practitioner are those of deaf dogs, dogs that house-soil because of renal, cardiovascular or gastrointestinal problems, and dogs that are aggressive because of a change in the number of animals or humans in the household or that are aggressive secondary to a chronic painful condition such as arthritis. Common feline problems may concern changes in the cat's environment. The treatment of behavioral problems of old animals is similar to the treatment of the problems of young animals, except that the physical limitations and disabilities of the old, usually ill, animal must be considered. Owners should be advised of the behavioral problems that may occur secondary to degenerative diseases and also be persuaded to keep social and environmental changes to a minimum in an old animal's life.