The aim of COSMOS is to carry out long-term health monitoring of a large group of people to identify if there are any possible health issues linked to using mobile phones and other wireless technologies over a long period of time. COSMOS NL is a part of the broader COSMOS study, which is being undertaken in six European countries: Denmark, Finland, Sweden, the Netherlands, France and the United Kingdom. More than 88,000 participants aged 19 to 87 years were recruited in the Netherlands from 2011 to 2012 as part of the LIFEWORK cohort. LIFEWORK was designed as a federated study also integrating the Nightingale Study, the Occupational and Environmental Health Cohort Study (AMIGO), and the European Prospective Investigation into Cancer and Nutrition in the Netherlands (EPIC-NL). Participants completed baseline assessment from 2011 to 2012. They are being followed up through questionnaires every four to five years and through linked data annually (including mobile phone and healthcare data). There are plans to follow the COSMOS cohort for up to 25 years or longer.