The environment in which we live greatly influences our health. One particular factor that has been related to morbidity and mortality is dwelling crowding. A range of mechanisms have been proposed as links between dwelling crowding and disease, including increased exposures to allergens, respiratory irritants and infectious agents in crowded dwellings. While studies of dwelling crowding have been conducted in many locations around the world, this factor has received little attention in Australian health studies. We examine relationships between dwelling crowding and health in Sydney, using three case studies at the local government area (LGA) level within the Sydney Statistical Division. Dwelling and demographic data from the 1996 Australian census are used, along with four socio-economic indexes produced by the Australian Bureau of Statistics, and hospital inpatient data for the period 1 July 1994 to 30 June 1997 as the health indicator. Results suggest that dwelling crowding is a significant factor in certain diseases in Sydney. Asthma hospital separations are not correlated with dwelling crowding, although multiple linear regression analysis produces three models which include crowding and three of the socio-economic indexes as significant variables. Separations for bronchitis and emphysema, and all causes combined, are positively correlated with dwelling crowding. Dwelling crowding is strongly negatively correlated with all but one of the socio-economic indicators.