•With good source control, <5 days of antibiotic therapy in surgery is recommended.•Compliance with this duration is low among the surgical community.•An ASP reduced the duration of treatment.•The ASP was implemented as part of a nosocomial infection surveillance programme.•Multidisciplinary teams including surgeons improve antibiotic stewardship. Guidelines recommend 5–7 days of antibiotic treatment in patients with surgical infection and adequate source control. This nationwide stewardship intervention aimed to reduce the duration of treatments in surgical patients to <7 days. Prospective cohort study evaluating surgical patients receiving antibiotics ≥7 days in 32 hospitals. Indication for treatment, quality of source control, type of recommendations issued, and adherence to the recommendations were analysed. Temporal trends in the percentages of patients with treatment >7 days were evaluated using a linear regression model and Pearson's correlation coefficients. A total of 32 499 patients were included. Of these, 13.7% had treatments ≥7 days. In all, 3912 stewardship interventions were performed, primarily in general surgery (90.7%) and urology (8.1%). The main types of infection were intra-abdominal (73.4%), skin/soft tissues (9.8%) and urinary (9.2%). The septic focus was considered controlled in 59.9% of cases. Out of 5458 antibiotic prescriptions, the most frequently analysed drugs were piperacillin/tazobactam (21.7%), metronidazole (11.2%), amoxicillin/clavulanate (10.3%), meropenem (10.7%), ceftriaxone (9.3%) and ciprofloxacin (6.7%). The main recommendations issued were: treatment discontinuation (35.0%), maintenance (40.0%) or de-escalation (15.5%), and the overall adherence rate was 91.5%. With adequate source control, the most frequent recommendation was to terminate treatment (51.2%). Throughout the study period, a significant decrease in the percentage of prolonged treatments was observed (Pc=-0.69;P < 0.001). This stewardship programme reduced the duration of treatments in surgical departments. Preference was given to general surgery services, intra-abdominal infection, and beta-lactam antibiotics, including carbapenems. Adherence to the issued recommendations was high. Display omitted