 Recruitment to the study took place between 1993 and 1999, and follow up is planned for at least ten years, with repeat interview/questionnaires every three to five years.The main prospective data collected are standardised dietary questionnaires (self-administered or interview-based), seven-day food diaries, blood samples and anthropometric measurements, such as body mass index and waist-to-hip ratio.Additionally, the GenAir case-control study is studying the relationship of passive smoking and air pollution with cancers and respiratory diseases.