The presence or absence of an extensive intraductal component (EIC) in early stage infiltrating ductal breast carcinoma has been considered to be an important factor in determining the extent of breast resection required prior to radiation therapy. It would therefore be useful if the presence or absence of an extensive intraductal component in a breast tumor could be predicted pre-operatively. To determine whether selected radiographic features might be correlated with whether or not a cancer is EIC+, we reviewed the pre-operative mammographic findings in 105 cases of Stage I and II infiltrating ductal carcinoma. Forty-one cases were EIC+ and 64 were EIC-. Both EIC+ and EIC- tumors were commonly detectable by mammography (93% and 83%, respectively, p = NS). EIC+ cancers, however, were significantly more likely to show microcalcifications with or without a mass compared to EIC- cases (83% vs 27%, p less than 0.0001). In particular, the presence of microcalcifications without a mammographic mass was more common for EIC+ cancers than EIC- cancers (34% vs 5% p = 0.0002). Conversely, a soft tissue mass without microcalcifications was seen mammographically in 56% of EIC- cases, compared to only 10% of EIC+ cases (p less than 0.0001). Predictive value calculations showed that the presence of microcalcifications in the absence of a mammographic mass conveys a 73% likelihood a cancer will be EIC+ (95% confidence interval = 39-94%). The positive predictive value of a mammographic mass or architectural distortion without microcalcifications for an EIC- cancer was 92% (95% confidence interval = 79-98%). We conclude that the mammographic findings may be useful pre-operatively in differentiating between patients with and without an EIC. Microcalcifications are much more commonly associated with EIC+ cancers than EIC- cancers, and the presence of an EIC- cancer without a mammographic mass is infrequent. Further characterization of the extent and pattern of microcalcifications might improve the predictive value of mammography in the pre-operative identification of patients with an EIC.