Methods: Clinicopathological characteristics, carried out local treatment strategies and adjuvant chemotherapy data were collected. Results: From 2001 to January 2006, 2754 Dutch patients were randomised to the study. Mean age of patients was 65 years (standard deviation 9). Tumours were < 2 cm in 46% (within CCCRs 39%-50%), node-negative disease varied from 25% to 45%, and PgR status was determined in 75%-100% of patients. Mastectomy was carried out in 55% (45%-70%), sentinel lymph node procedure in 68% (42%-79%) and axillary lymph node dissections in 77% (67%-83%) of patients, all different between CCCRs (P < 0.0001). Adjuvant chemotherapy was given in 15%-70% of eligible patients (P < 0.001). Discussion: In spite of national guidelines, breast cancer treatment on specific issues widely varied between the various Dutch regions. These data provide valuable information for breast cancer organisations indicating (lack of) guideline adherence and areas for breast cancer care improvement.