(1) A method of study is presented to determine the prognosis in carcinoma of the breast. This considers both the clinical extent of the carcinoma and the histologic study. (2) A new clinical classification depending upon the extent of the growth is discussed. (3) The histologic classification of Haagensen is used. (4) This study is based on 75 cases of proved carcinoma of the breast. (5) The most important factors in determining prognosis are delay in institution of treatment and the extent of the disease. (6) The histologic classification seems to be of less importance than the clinical study, but has a definite value. (7) No attempt has been made to determine the value of various forms of treatment. (8) it is realized that this series of cases is quite small. It is hoped that this method of study may be adopted at larger clinics so that a greater number of cases may be followed.