The most important factor in improving the survival rates of the patients with breast cancer is early detection. A high cure rate can be expected if the condition is discovered in early stage. There were 195 patients with primary breast cancer in our hospital from August 1978 to November 1986. Among 280 patients with breast cancer who received radical operations from July 1970 to November 1986, there were 50 patients (18%) with recurrence. Mammography and echography were effective for the diagnosis of infiltrating cancer smaller than 10mm in diameter as well as those between 11 and 20mm in diameter. None of the patients with non-infiltrating or infiltrating carcinomas smaller than 15 mm or smaller than 20 mm in diameter with negative nodes had recurrence. Consequently, at present we define early breast cancer as the lesions of pathologically noninfiltrating or infiltrating smaller than 15 mm in diameter, or infiltrating smaller than 20 mm in diameter with negative nodes.