To allocate sufficient resources to clinical services or to research and development in the most effective way possible, statistics are needed on the prevalence of the condition in question for various degrees of severity. For the United Kingdom, such data for tinnitus have become available from two recent large-scale studies. The first is the National Study of Hearing (NSH) which is being conducted by the Medical Research Council's Institute of Hearing Research from its headquarters in Nottingham and its clinical outstations in Cardiff, Glasgow, Nottingham and Southampton. It started in 1978 and is now entering its third phase. The second study is the General Household Survey carried out in 1981 by the UK Office of Population Censuses and Surveys (OPCS). The rationale and methodology of the NSH and the prevalence data obtained up to the present, together with those from the OPCS survey, will be given in this paper; the demographic data and the clinical aspects of the study will be presented in the accompanying paper (IHR, 1984).