From mathematical treatment of the results of operative treatment of 163 patients with acute cholecystitis on a computer with the use of program complexes on the basis of the mathematical theory of image recognition the authors obtained a decisive rule which allowed calculation of the prognostic index reflecting the severity of the patient's condition and the prognosis of the surgical treatment according to the initial values of total protein, leucocytosis, AlAT, and the patient's age. Besides, the efficacy of the preoperative management can be judged from the dynamics of changes of the index. Development of the tactics of treatment of patients with acute cholecystitis on the basis of the prognostic index improved the results of operative treatment considerably.