The purpose of this study was to describe the anemia of inflammatory disease (AID) in cats with naturally-occurring inflammatory diseases, such as abscesses (n = 12), pyothorax (n = 6), and fat necrosis (n = 3). Exclusion criteria were positive FeLV/FIV tests, neoplasia, nephro-, hepato- or endocrinopathies, and blood loss anemia. CBC, clinical biochemistry, measurements of serum erythropoietin, iron, total iron-binding capacity (TIBC), ferritin, acute phase proteins, erythrocytic osmotic fragility (OF), and Coombs' tests were performed. A decrease in hematocrit of 1-28% (median, 10%) occurred within 3-16 days (median, 8 days). The anemia was mild (n = 11), moderate (n = 8), or severe (n = 2). In most cases it was normocytic normochromic, non-regenerative (n = 18), or mildly regenerative (n = 3). Sixteen cats had leukocytosis and 5 mild hyperbilirubinemia. The Coombs' test results were negative for 8 cats and positive for 1 cat. OF was increased in 2 out of 14 cats. Hypoalbuminemia (n = 18) and hyperglobulinemia (n = 16) resulted in a lowered albumin/globulin-ratio in 19 cats. Iron and TIBC were low in 2/19 and 6 /19 cats, respectively. The ferritin concentrations were normal in 7 cats and increased in 12 cats. The acute phase proteins alpha1-acid-glycoprotein and haptoglobin were increased in 14/14 and 13/14 cats, respectively. Erythropoietin was normal (n = 4), mildly increased (n = 7) or severely increased (1). Two cats were euthanized due to their underlying disease, 3 cats needed blood transfusions. AID in cats is usually mild to moderate, non-regenerative, and normocytic normochromic. It can be clinically relevant causing severe and transfusion-dependent anemia. AID seems to be multifactorial with evidence of iron sequestration, decreased RBC survival, and insufficient erythropoietin production and bone marrow response. Specific and supportive therapy, including transfusions, can reverse these processes.