It is difficult to give the prognosis of diabetes mellitus after castration of the bitch. An algorithm using the blood glucose and fructosamine level is suggested to evaluate the prognosis of diabetes: While the algorithm classifies 19 bitches with good prognosis 18 (95%) are cured. 18 are classified with poor prognosis and all of them undergo a long difficult insulin-therapy or are not treated with success. 6 bitches are classified as indifferent, 2 of them are cured by castration, 2 are managed with insulin and 2 are treated without success. The limits can be described by the following equations: lower limit y = 5.04x + 321, upper limit y = 7.74x + 433. If blood glucose is available only in mg/dl, the equations are: lower limit y = 0.28 + 321, upper limit y = 0.43x + 433. The algorithm is statistical high significant but it should be verified by calculation of a larger number of patients.