This study is concerned with the specific associa tion of housing conditions with the prevalence of tuberculosis as found in a 3-year survey by a static Mass Radiography Unit in the Metropolitan Borough of Islington (Brett, Benjamin, Craig, Wallace, and Freeman, 1956). It does not attempt to examine this association from the point of view of the spread of tuberculosis once an infector is intro duced into the household; it is solely concerned with the question whether poor housing, as one of the elements of poverty, does in fact have any specific bearing on the incidence of the disease. It was thought that an analysis of individual households in relation to tuberculosis might be of value in view of earlier studies (Stein, 1952; Benjamin, 1953) based on the relationship between morbidity or mortality rates and general housing conditions as revealed in censuses or surveys in local authority areas or sub divisions thereof, the whole area being ranked by those indices without any specific relationship between the households which were tuberculous and those whicji were overcrowded.