Glycated hemoglobin (GHb) and fructosamine were measured in diabetic and nondiabetic cats to determine if these parameters are useful in monitoring long-term glycemic control in cats with diabetes mellitus. A total of 24 diabetic and 30 nondiabetic cats were evaluated over a six-month period. Mean percentage GHb for group 1 (n = 13) healthy cats (8.3 +/- 2.6), group 2 (n = 17) cats with nondiabetic illnesses (6.8 +/- 2.4), and group 3 (n = 10) well-regulated diabetic cats (9.1 +/- 2.5) were significantly lower than for group 4 (n = 14) untreated and poorly regulated diabetic cats (13.6 +/- 3.6). Mean fructosamine values (mMol/L) for group 1 (n = 8) (2.1 +/- 0.3) and group 2 (n = 2) (1.9 +/- 0.4) also were significantly lower than for group 4 (n = 6) (3.9 +/- 0.9); however the mean for group 3 (n = 12) (3.3 +/- 1.2) was not significantly different than for group 4. The correlation coefficient between percentage GHb and fructosamine for an individual was 0.34. Diabetic cats showing clinical improvement had reductions in percentage GHb of 0.6% to 2.6% per week. Glycated hemoglobin is a clinically useful tool in diagnosis and management of feline diabetes mellitus, but fructosamine is not.