Background: The aim of centralizing rectal cancer surgery in Catalonia (Spain) was to improve the quality of patient care. We evaluated the impact of this policy by assessing patterns of care, comparing the clinical audits carried out and analysing the implications of the healthcare reform from an organizational perspective. Methods: A mixed methods approach based on a convergent parallel design was used. Quality of rectal cancer care was 25 assessed by means of a clinical audit for all patients receiving radical surgery for rectal cancer in two time periods (2005-2007 and 2011-2012). The qualitative study consisted of 18 semi-structured interviews in September- December 2014, with healthcare professionals, managers and experts. Results: From 2005-2007 to 2011-2012, hospitals performing rectal cancer surgery decreased from 51 to 32. The proportion of patients undergoing surgery in high volume centres increased from 37.5% to 52.8%. Improved report of total mesorectal excision 30 (36.2 vs. 85.7), less emergency surgery (5.6% vs. 3.6%) and more lymph node examinations (median: 14.1 vs. 16) were observed (P < 0.001). However, centralizing highly complex cancers using different critical masses and healthcare frameworks prompted the need for rearticulating partnerships at a hospital, rather than disease, level. Conclusion: The centralization of rectal cancer surgery has been associated with better quality of care and conformity with clinical guidelines. However, a more integrated model of care delivery is needed to 35 strengthen the centralization strategy.