Six hundred and two mammary tumors were examined clinically, by mammography and cytology, with a histologic checkup following surgical biopsy. There were 247 cases of malignoma and 355 benign cases. The limited reliability of the individual methods is demonstrated, and it is shown that their combined use can improve the diagnosis. More malignomas are detected, and preoperative diagnosis is made more safely. If all three methods yield identical results, as was the case in 50.2% of the malignant and 32.7% of the benign lesions, the probability of diagnostic error is less than one per cent. With a malignoma thus established, surgical treatment may follow immediately, or irradiation can be started. In benign cases a surgical biopsy may be foregone and further developments may be awaited with due provision for regular control. If the three methods yield conflicting or doubtful results, elucidation by surgical biopsy and histology is indicated.