In 1986, a prospective cohort study on diet and cancer was started in The Netherlands. The cohort (n = 120, 852) of 55-69 year old men (48.2%) and women (51.8%) originates from 204 computerized municipal population registries. At baseline, participants completed a self-administered questionnaire on diet and potential confounding variables. In addition, about 67% of the participants provided toenail clippings. Cancer follow-up consists of record linkage to a pathology registry and to cancer registries. The initial interest is in stomach, colorectal, breast and lung tumors. A case-cohort approach is applied, in which detailed follow-up information of a random subcohort (n = 5000) provides an estimate of the person-time experience of the cohort. Exposure data of the subcohort will be combined with those of incident cases, yielding exposure-specific incidence rate ratios. The intraindividual variation in determinants is estimated by annually repeated measurements (n = 250) within the subcohort. The rationale, efficiency aspects and study characteristics are discussed.