Suppose that a cohort of individuals is to be followed in order to relate failure rates to preceding covariate histories. A design is proposed which involves covariate data only for cases experiencing failure and for members of a randomly selected ubcohort. Odds ratio and relative risk estimation procedures are presented for such a ‘case-cohort’ design. A small simulation study compares ease-cohort relative risk estimation procedures to full-cohort and synthetic case-control analyses. Relevance to epidemiologic cohort studies and disease prevention trials is discussed.