Biopsy of the breast for mammographically detected lesions. We prospectively studied 718 women who underwent biopsy of the breast for suspicious, mammographically detected mammary lesions in an attempt to identify key clinical risk factors, as well as roentgenographic characteristics associated with the appearance of early carcinoma of the breast. Patients with a benign outcome had an average age of 55 years versus 63 years for patients with carcinoma of the breast. Seventy-six per cent of these patients had no previous history of mammary problems, 20 per cent had a positive family history for carcinoma of the breast, 58 per cent were premenopausal and 21 per cent had used birth control pills. Except for age (p less than 0.001), the distribution of clinical risk factors was equal among patients with benign or malignant outcomes. Suspicious mammographic findings included mass lesions (53 per cent), calcifications (36 per cent) and the association of both (11 per cent). The predominant Wolfe pattern on mammography was P1 (36 per cent). No relationship was observed between Wolfe pattern and malignant conditions. In this group of patients, mammography was poorly specific; however, the positive predictive value increased with age and is related to the age-specific prevalence of carcinoma of the breast. Eight hundred and twenty-five lesions were removed. Twenty-five per cent (n = 203) of the specimens taken at biopsy contained carcinoma. Stellate mass lesions were highly suggestive of a malignant growth (p less than 0.0001). No relationship between the size of the suspicious mammographic mass and the malignant lesion was observed. A marked correlation (chi-square test with Yate's correction) was observed between malignant tumor and lesions with a linear or branching pattern, more than 15 calcifications, or small sized calcifications. The presence of a mass with calcifications was associated with carcinoma in 34 per cent. The incidence of invasive carcinoma was much higher for mass lesions (81 per cent) than for suspicious calcifications (56 per cent) (p less than 0.0001). 