Most important is elimination or "bathroom" behavior. In order for a cat to successfully use a litter box, he must first register the need to urinate or defecate, then make his way to the nearest litter box and negotiate its rim or cover. As with dogs, appropriate elimination habits may be one of the first behaviors to deteriorate in elderly cats. And, as with all elderly animals, it is particularly important to exclude medical conditions contributing to an abnormal increased production of urine, for example, diabetes, poor kidney function, or hyperthyroidism.
Whether or not medical problems are involved, there are simple steps worth taking to ease the stress of aging. First, consider providing additional litter boxes in easily accessible areas. Don't expect your elderly cat to climb stairs, up or down, or to find boxes hidden a little too well. Also helpful is the use of boxes with lower sides, or even trays, to minimize the need for climbing.
Cats, like dogs, may exhibit other unusual behaviors as they age. In addition to inappropriate elimination, they may show changes in their social relationships and increased vocalization. Close medical monitoring will help distinguish between normal aging and situations in which cats show senile behavior changes much like those in dogs and humans.