PURPOSE: To examine the availability and quality of clinical guidelines on perioperative diabetes care in hospital units before and after a randomised clinical trial (RCT) and international accreditation. DESIGN/METHODOLOGY/APPROACH: Interventional "before-after" study in 51 units (38 surgical and 13 anaesthetic) in nine hospitals participating in a RCT in the greater Copenhagen area; 27 of the units also underwent international accreditation. FINDINGS: The proportion of units with guidelines increased from 24/51 (47 percent) units before to 38/51 (75 percent) units after the trial. Among the 27 units without guidelines before the trial, significantly more accredited units compared to non-accredited units had a guideline after the trial (9/10 (90 percent) compared to 5/17 (29 percent). The quality of the systematic development scale and the clinical scales improved significantly after the trial in both accredited units (both p