Immune-mediated hemolytic anemia (IMHA) occurs less frequently in cats than in dogs. The value of the Coombs' test (CT) has been questioned, but detailed surveys of its use are lacking. The objective of this study was to describe 19 cats with primary IMHA (pIMHA) and to examine the diagnostic value of the direct CT. The CT was performed in 92 cats; it was negative in 5 healthy, in 9 sick nonanemic, and in 55 cats with different types of anemia. The CT was positive in 18 anemic cats (2 feline leukemia virus (FeLV) positive, 1 with cholangiohepatitis, 15 with no underlying disease). Moreover, agglutination persisted after saline washing in 5 anemic cats (1 lymphoma, 4 pIMHA). Inclusion criteria for pIMHA were a positive CT (15) or persistent agglutination (4), and the exclusion of other diseases. The age of the 19 cats ranged from 0.5 to 9 years (median, 2 years); male cats were overrepresented. The PCV on admission was 6-22% (median, 12%). The anemia was nonregenerative in 11 cats. Additional abnormal laboratory results were leukocytosis (2), lymphocytosis (6), hyperbilirubinemia (13), hyperglobulimemia (10), and increased liver enzyme activities (10). Initial treatment consisted of blood transfusions (10), crystalloids (11), prednisolone (19), antibiotics (19), and H2-blockers (11). Four of 17 cats were euthanized 9, 63, 240 and 2,160 days after initial presentation (mortality rate, 23.5%). Relapses were reported in 5 of 16 cases (31%). Thus, pIMHA appears to occur more frequently than recognized previously, with a more favorable prognosis in cats than in dogs. The CT was useful in identifying immune-mediated pathogenesis.