Objectives To describe how adverse event (AE) rates were monitored and estimated nationally across all Norwegian hospitals from 2010 to 2013, and how they developed during the monitoring period. Monitoring was based on medical record review with Global Trigger Tool (GTT).

Setting All publicly and privately owned hospitals were mandated to review randomly selected medical records to monitor AE rates. The initiative was part of the Norwegian patient safety campaign, launched by the Norwegian Ministry of Health and Care Services. It started in January 2011 and lasted until December 2013. 2010 was the baseline for the review. One of the main aims of the campaign was to reduce patient harm.

Method To standardise the medical record reviews in all hospitals, GTT was chosen as a standard method. GTT teams from all hospitals reviewed 40 851 medical records randomly selected from 2 249 957 discharges from 2010 to 2013. Data were plotted in time series for local measurement and national AE rates were estimated, plotted and monitored.

Results AE rates were estimated and published nationally from 2010 to 2013. Estimated AE rates in severity categories E-I decreased significantly from 16.1% in 2011 to 13.0% in 2013 (−3.1% (95% CI −5.2% to −1.1%)).

Conclusions Monitoring estimated AE rates emerges as a potential element in national systems for patient safety. Estimated AE rates in the category of least severity decreased significantly during the first 2 years of the monitoring.