ObjectiveTo evaluate the effects of external inspections on (1) hospital emergency departments’ clinical processes for detecting and treating sepsis and (2) length of hospital stay and 30-day mortality.DesignIncomplete cluster-randomised stepped-wedge design using data from patient records and patient registries. We compared care processes and patient outcomes before and after the intervention using regression analysis.SettingNationwide inspections of sepsis care in emergency departments in Norwegian hospitals.Participants7407 patients presenting to hospital emergency departments with sepsis.InterventionExternal inspections of sepsis detection and treatment led by a public supervisory institution.Main outcome measuresProcess measures for sepsis diagnostics and treatment, length of hospital stay and 30-day all-cause mortality.ResultsAfter the inspections, there were significant improvements in the proportions of patients examined by a physician within the time frame set in triage (OR 1.28, 95% CI 1.07 to 1.53), undergoing a complete set of vital measurements within 1 hour (OR 1.78, 95% CI 1.10 to 2.87), having lactate measured within 1 hour (OR 2.75, 95% CI 1.83 to 4.15), having an adequate observation regimen (OR 2.20, 95% CI 1.51 to 3.20) and receiving antibiotics within 1 hour (OR 2.16, 95% CI 1.83 to 2.55). There was also significant reduction in mortality and length of stay, but these findings were no longer significant when controlling for time.ConclusionsExternal inspections were associated with improvement of sepsis detection and treatment. These findings suggest that policy-makers and regulatory agencies should prioritise assessing the effects of their inspections and pay attention to the mechanisms by which the inspections might contribute to improve care for patients.Trial registrationNCT02747121.