The aim of this report was to analyse positive and negative aspects of online administration of longitudinal well-being survey and to provide suggestions and guidelines for future research. The aim of CRO-WELL (Croatian Longitudinal Wellbeing Study) research was to follow well-being indicators longitudinally, on a large sample (N>5 000).For the purpose of the research we developed online platform with integrated questionnaire to assess various variables related to well-being. Participants could assess the application via various browsers, and it was also adjusted for smart phones. "Friendly use" of the online application, understanding of questions and answering method, as well as ethical concerns, was tested using focus groups and individual trials. To enable matching the participants from two waves, every participant had to log in to the web