Aims: The New Zealand Surgical Site Infection Improvement (SSII) Programme was established in 2013 to reduce the incidence of surgical site infections (SSI) in publicly funded hip and knee arthroplasties in New Zealand hospitals., Methods: The programme pursued a three-pronged strategy: 1. Surveillance of SSI with a nationwide system 2. Promotion of consistent adherence to evidence-based practices proven to reduce SSI 3. Monitoring and publicly reporting changed practice and outcome data., Results: Between quarter 3 2013 and quarter 4 2016 there has been a nationwide increase in compliance with all process measures: correct timing for antibiotic prophylaxis; use of the recommended antibiotic in the recommended dose and alcohol-based skin antisepsis. The SSI rate in hip and knee arthroplasties has shown a significant improvement. The nationwide median rate has fallen to 0.91% since June 2015, compared with 1.36% during the baseline period of April 2013 to March 2014 (p<0.01). This equates to approximately 55 fewer infections between August 2015 and June 2017, savings of NZD$2.2 million in avoided treatment and avoided disability-adjusted life years (DALYs) of NZD$5 million., Conclusions: The introduction of a nationwide SSI reduction programme for hip and knee arthroplasties resulted in an increase in compliance across the country with best practice that was associated with a reduction in incidence of SSI since June 2015 from the baseline period of April 2013 to March 2014, sustained to June 2017., Competing Interests: Richard Hamblin and Carl Shuker report affiliation with Health Quality & Safety Commission during the conduct of the study. Arthur Morris states that he is the Clinical Lead for the NZ Surgical Site Infection Improvement Programme. Sally Roberts is the National Clinical Lead for Health Quality and Safety Commission Infection Prevention and Control Programme. Alan Merry reports affiliation with Safer Sleep LLC, from null, outside the submitted work; and is Chair of Board of Health Quality and Safety Commission in New Zealand.