Improved early diagnosis and utilization of new procedures for postoperative treatment of breast cancer have made it possible, especially in the case of small tumors, to depart from the orthodox radical operative procedures. In planning a proper therapeutic approach, preoperative diagnosis plays an ever increasing role. In a prospective study 103 cases with cytologically and histologically verified carcinoma of the breast were subjected to cytological grading. The parameter for the grading included the dissociation range and polymorphism of the nuclei, the occurrence of nucleoli and the size of the nuclei. The low-risk-group was comprised mainly of older patients with small cell unimorphous, histologically scirrhous or tubular carcinomas. The high-risk-group was comprised mainly of younger patients predominantly with large call polymorphous, histologically solid carcinomas. The results are expected to give insight into tumor dynamics as well as to be to of therapeutic relevance.