To determine the number and duration of nosocomial outbreaks caused by highly resistant microorganisms (HRMO) posing a potential threat to public health, in order to undertake a risk assessment.Descriptive study.Data on nosocomial outbreaks were collected from April 2012 to June 2014. The following characteristics were recorded at the start and end of each outbreak: type of microorganism, reason for reporting, phase of outbreak, number of patients colonised and infected, and infection prevention measures implemented.47 medical institutions reported 87 outbreaks (mean: 3 outbreaks per month). 20 outbreaks were reported in 2012 (2.2/month), 39 in 2013 (3.3/month), and 28 in the first six months of 2014 (4.7/month). Outbreaks of vancomycin-resistant enterococci (n = 26), methicillin-resistant Staphylococcus aureus (MRSA; n = 23) and resistant or highly resistant Enterobacteriaceae (n = 17) were reported most frequently. 65 outbreaks (75%) were controlled within two months of reporting.Transparent reporting of HRMO outbreaks is important for correct public perceptions of the safety of hospitals and nursing homes in the Netherlands. Reports to the Hospital-acquired Infection and Antimicrobial Resistance Monitoring Group show that HRMO outbreaks are an almost daily occurrence in Dutch hospitals. However, most outbreaks are quickly controlled without posing a threat to public health.