Fears have been expressed in the House of Representatives that health insurers may be applying risk selection by offering health insurance policies targeted specifically at foreign seasonal workers. The aim of this study is to ascertain whether there are clear and complete records of foreign seasonal workers. The answer is yes, there are. The simplest way of identifying foreign seasonal workers is by supplementing data from the current Risk Adjustment Research Working Group database with nationality data from the Personal Records and Travel Documents Agency. For more precise identification this can be supplemented with data on employees from the UWV (Employee Insurance Agency) and data on the self-employed from the Tax and Customs Administration.