We performed a quality improvement initiative to reduce unnecessary treatments for acute bronchiolitis (AB) in primary care (PC) and the referral paediatric emergency department (ED). The quality improvement initiative involved two seasons: 2016–2017 (preintervention) and 2017–2018 (postintervention). We distributed an evidence-based protocol, informative posters and badges with the slogan ‘Bronchiolitis, less is more’. We also held interactive sessions, and paediatricians received weekly reports on bronchodilator prescription. The main outcome was the percentage of infants prescribed salbutamol. Secondary outcomes were epinephrine, antibiotic and corticosteroid prescription rates. Control measures were ED visit and hospitalisation rates, triage level, length of stay, intensive care admission and unscheduled returns with admission. We included 1878 ED and 1192 PC visits of which 855 (44.5%) and 534 (44.7%) occurred in the postintervention period, respectively. In the ED, salbutamol and epinephrine prescription rates fell from 13.8% (95% CI 11.8% to 16%) to 9.1% (95% CI 7.3% to 11.2%) (p<0.01) and 10.4% (95% CI 8.6% to 12.4%) to 9% (95% CI 7.2% to 11.1%) (n.s.), respectively. In PC, salbutamol, corticosteroid and antibiotic prescription rates fell from 38.3% (95% CI 34.6% to 42.0%) to 15.9% (95% CI 12.9% to 19.5%) (p<0.01), 12.9% (95% CI 10.5% to 15.7%) to 3.6% (95% CI 2.2% to 5.7%) (p<0.01) and 29.6% (95% CI 26.2% to 33.2%) to 9.5% (95% CI 7.2% to 12.5%) (p<0.01), respectively. No significant variations were noted in control measures. We safely decreased the use of unnecessary treatments for AB. Collaboration between PC and ED appears to be an important factor for success.