The TREAT NL (TREatment of ATopic eczema, the Netherlands) registry is a national registry for children and adults with moderate-to-severe atopic eczema aiming to gather data on their prescribed photo- and systemic immunomodulating therapies. Atopic eczema is a common, chronic, itchy, inflammatory skin disease that can have a major impact on the quality of life of patients and their immediate surroundings. Serious atopic eczema patients are treated by means of photo- or systemic immunomodulating therapy. Of these mostly off-label applied therapies, there is insufficient evidence on the short and long term for their effectiveness, safety and cost-effectiveness. Moreover, good comparative research and real-life data are lacking. With the arrival of new expensive treatments it is crucial to get insight into these treatments in order to improve quality of care. By means of a prospective registry these data can be collected and help to obtain information for clinical practice, for answering research questions, for reducing costs and implementing the results by guidelines and decision aids.