Guidelines are tools to improve the quality of care in daily practice. To accomplish adherence, active implementation is needed. The effect of audit, group-oriented feedback and educational activities to increase guideline adherence were investigated in this study. Treatment according to a guideline for premenopausal node-positive breast cancer patients from 1988 to 1992 (PI) and from 1996 to 1998 (P2) was assessed using the following indicators: percentage of patients with breast-conserving surgery, secondary surgery, greater than or equal to10 reported resected axillary lymph nodes, reported tumour differentiation grade, reported hormonal receptor status, chemotherapy received (CT), start of CT less than or equal to28 days after surgery, Dose Intensity (DI) greater than or equal to85% and completion of CT less than or equal to1 week beyond the ideal duration of CT. Data were audited from patients' records. The first audit resulted in a quality programme with feedback focused on the delivery of chemotherapy and resected axillary lymph nodes and educational sessions. A Fisher's exact test was used to estimate significant differences between the two time periods. In PI, 323 patients and in P2, 155 patients were eligible for treatment according to the guideline. The percentage of patients with greater than or equal to10 lymph nodes improved from 65.3 to 81.3% (P=0.0004), as did the percentage with a reported oestrogen receptor (ER) status, from 84.8 to 96.8% (P=0.00004), progesterone receptor (PR) status from 82.3% to 97.4% (P<0.000001) and with a DI greater than or equal to85%, from 74.9 to 93.9% (P=0.000003). Adherence varied between the hospitals. In conclusion, significant improvements were observed for the indicators of resected axillary lymph nodes and DI of chemotherapy, which may be attributed to the quality programme. Repeated assessment of the adherence to the guideline is important to observe changes and interhospital variations in order to remain focused on areas for improvement. (C) 2003 Elsevier Ltd. All rights reserved.