BACKGROUND A concordant triple assessment (clinical, mammographic and cytological) diagnosis of breast malignancy allows for pre-operative planning of surgery and may also allow for one-stage surgery. However, while the accuracy of cytology is high, it is unable to distinguish invasive cancer from ductal carcinoma in situ (DCIS). A malignant mass may be due to pure in situ cancer and hence axillary dissection may be avoided if pre-operative histology is available. METHODS A consecutive series of 300 cases of breast cancer treated over the last 5 years by the two authors was analysed to determine: the method of achieving pre-definitive operation histology; the number of stages of surgery required; and the number of cases of mass-forming DCIS which could be susceptible to over-treatment. RESULTS Of 289 patients undergoing local definitive surgery for breast cancer, 12 (42%) had clinical masses predominantly due to DCIS and in most of these patients axillary dissection was avoided. Histology was obtained prior to definitive surgery in 272 (94.1%) patients, by intra-operative frozen section in 159 (55.0%), incisional biopsy in 37 (12.8%), needle localization biopsy in 62 (21.5%) and core biopsy in 14 (4.8%). A total of 189 patients (65.4%) underwent one-stage surgery only. Breast conservation was achieved in 210 (72.7%) patients. Those requiring mastectomy were significantly more likely to have required two stages of surgery as were those with lesions detected by screening. CONCLUSIONS Mass-forming DCIS cannot be predicted pre-operatively by triple assessment alone; and therefore pre-operative histology is required to avoid axillary dissection. Pre-operative histology may be obtained by core biopsy or intra-operative frozen section to identify DCIS and distinguish it from invasive disease, but both allow a one-stage surgical procedure in the majority of cases.