In breast conservation therapy, the margin status of the specimen predicts local recurrence and determines the need for reexcision. Many surgeons now take, at the time of lumpectomy, multiple separate "cavity margins" (CM) (the entire wall of the residual cavity) as final margins that supersede the oriented lumpectomy margins (LMs). We studied the efficacy of this method in 126 patients (23 with ductal carcinoma in situ [DCIS] only and 103 with invasive carcinoma with or without DCIS) who had an oriented lumpectomy specimen and also had four to six additional CMs. The tumors were evaluated for the following: size, grade, LM status (distance of tumor from margin and, if involved, extent of involvement), vascular invasion, lymph node status, and presence or absence of extensive intraductal component. The additional CM specimens were evaluated for residual carcinoma (if any) and its distance from the inked true margins, and the results were correlated with the corresponding LMs. Only approximately 50% of patients (52 of 103) with histologically positive LMs (defined as carcinoma within 2 mm of the inked surface) had residual carcinoma in their CMs. Additional CM sampling rendered the overall final margin status histologically negative in 61 of 103 (59%) cases with histologically positive LMs, therefore significantly reducing the need for reexcision. Younger patient age, higher number of positive LMs, high tumor grade, and the presence of extensive intraductal component were predictive of residual carcinoma in CM specimens, whereas the distance of carcinoma from the inked surface and the extent of tumor involvement of histologically positive LMs were not. Because CM specimens taken from patients with histologically positive LMs usually lack tumor, we suspect that many positive LMs are likely false positives. Possible factors accounting for false-positive LMs include seepage of ink into crevices of the specimen promoted by excessive inking, tumor friability promoting displacement of tumor into ink, manipulation of specimens for radiographs, and retraction artifact.