Medical care is increasingly a technical business, and hospitalised patients are more and more susceptible to infections, notably due to the application of aggressive therapies for all kinds of disorders. As a consequence the epidemiology of hospital infections requires serious attention. Following the initiative of some medical microbiologists in the Netherlands, a study group was established to tackle this epidemiology and to initiate relevant research (Working party on Hospital Infections and Epidemiology of the Netherlands; WHEN). Recent subjects include fungemia in hospitalised patients, risk factors for acquiring methicillin-resistant Staphylococcus aureus during a stay abroad, and prevalence of vancomycin-resistant enterococci.