BACKGROUND: People who inject drugs face several health issues because of unsafe injecting practices. We aimed to evaluate changes in supervised drug-injecting practices following the implementation of a face-to-face educational intervention. METHODS: The national study ANRS-AERLI was conducted in 17 harm reduction (HR) facilities in France between 2011 and 2013. Eight offered the intervention and nine did not. We conducted a pre-post analysis focusing on injecting practices data, collected in the 8 HR facilities providing the intervention. The intervention consisted of providing face-to-face educational sessions including direct observation of injecting practices, counseling about safer injecting, and shared discussion. Injecting practices were collected following a checklist and classified as safe or unsafe. To assess changes in injecting practices, practices were compared before (at baseline) and after at least one educational session. FINDINGS: Mixed logistic models showed that the 78 participants included were more likely to improve in the following drug-use steps: setting up a clean preparation area (Adjusted Odds Ratio (AOR) = 3.4, 95% Confidence Interval (95% CI) = 1.6-7.6), hand washing (AOR = 7.2, 95% CI = 3.1-16.4), skin cleaning (AOR = 5.6, 95% CI = 2.5-12.1), choice of safe injection site (AOR = 6.5, 95% CI = 1.5-28.8) and post-injection bleeding management (AOR = 12.8, 95% CI = 5.5-29.9). Furthermore, participants were less likely to lick their needles before injecting (AOR = 8.1, 95% CI = 1.5-43.4) and to perform booting/flushing (AOR = 2.5, 95% CI = 1.2-5.3). CONCLUSIONS: The AERLI intervention seems to be effective in increasing safe drug-injecting practices.