The characteristics of feline mammary cancer--that is, the rapid growth of primary mammary tumors, the high rate of tumor recurrence, and the poor survival statistics--demonstrate the need for (1) early diagnosis of the primary tumor; (2) immediate, aggressive surgical therapy; and (3) frequent follow-up examinations to detect early clinical signs of recurrent disease. A number of factors that influence prognosis have been described. As more information becomes available concerning the behavior of feline mammary tumors and the results of various forms of treatment, more effective protocols can be developed. Continued etiologic research may play a vital role in determining the direction of therapy.