A national reporting system for patient safety incidents (PSI) was introduced in Denmark in 2004. This article describes the experience of the first five years of reporting. The Danish reporting system has the following characteristics: Reporting is mandatory for all healthcare professionals employed at hospitals; reporting is confidential with an option for anonymous reporting; reporting takes place in a non-punitive system. It is concluded that PSI reporting is an important element of a mature safety culture and an important source for qualitative data on an organization's patient safety performance.