The aim of this study was to develop a standardised surgical report for breast-conserving procedures, supporting the systematic documentation of the different aspects of the surgery. The surgical procedure for tumourectomy and axillary clearance was translated into a series of steps that could be quantitatively documented. This description was submitted twice to a group of surgeons from different departments to ensure that all steps that are considered to have relevance for outcome were included and that no superfluous data were collected. After two corrective phases, a first test format was developed. Between February 1993 and May 1994, seven surgical departments, participating in EORTC trials, completed this questionnaire for a number of their patients. The data collected related to general information on the department, the tumour excision itself, the axillary dissection and, in a later phase, on pathology. 269 questionnaires (264 tumour excisions, 259 axillary dissections and 189 pathology reports) were collected and analysed. Even though the participating departments were involved in a single trial on breast-conserving surgery and had previously developed regular contacts about the practical aspects of treatment, many differences were detected. In general, variations were found in the waiting time between treatment prescription and execution, experience of the surgeon, duration of the procedure, and the use of prophylactic antibiotics. Also, in the practical execution of the procedure, major variations in the type of incision, width of tumour excision, closure of the breast tissue and skin, the use of frozen sections and the extent of the axillary dissection were found. The most relevant differences and their possible consequences are discussed. It has been proven possible and feasible to document quantitatively a surgical procedure. The fact that within a group of surgeons participating in the same clinical trials, many differences in the surgical techniques are observed, stresses the need to reach a consensus on a stricter set of guidelines for breast-conserving procedures and their documentation, especially when conducting clinical trials.