OBJECTIVE: To classify ipsilateral breast tumor recurrences (IBTR) as either new primary tumors (NP) or true local recurrence (TR). We utilized 2 different methods and compared sensitivities and specificities between them. Our goal was to determine whether distinguishing NP from TR had prognostic value. BACKGROUND: After breast-conservation therapy, IBTR may be classified into 2 distinct types (NP and TR). Studies have attempted to classify IBTR by using tumor location, histologic subtype, DNA flow cytometry data, or gene-expression profiling data. METHODS: A total of 447 (7.9%) of 5660 patients undergoing breast-conservation therapy from 1970 to 2005 experienced IBTR. Clinical data from 397 patients were available for review. We classified IBTRs as NP or TR on the basis of either tumor location and histologic subtype (method 1) or tumor location, histologic subtype, estrogen receptor status and human epidermal growth factor receptor 2 status (method 2). Kaplan-Meier curves and log-rank tests were used to evaluate overall and disease-specific survival differences between the 2 groups. Classification methods were validated by calculating sensitivity and specificity values using a Bayesian method. RESULTS: Of 397 patients, 196 (49.4%) were classified as NP by method 1 and 212 (53.4%) were classified as NP by method 2. The sensitivity and specificity values were 0.812 and 0.867 for method 1 and 0.870 and 0.800 for method 2, respectively. Regardless of method used, patients classified as NP developed contralateral breast carcinoma more often but had better 10-year overall and disease-specific survival rates than those classified as TR. Patients with TR were more likely to develop metastatic disease after IBTR. CONCLUSION: Ipsilateral breast tumor recurrences classified as TR and NP had clinically different features, suggesting that classifying IBTR may provide clinically significant data for the management of IBTR.