We set out to investigate the extent to which cultural constructs might determine treatment-seeking for diarrhoea in the poorer populations of Lusaka, Zambia. This paper describes these concepts and perceptions and outlines a classification of such illnesses, together with an analysis of its implications for understanding treatment choice. Data were derived from focus group discussions, a household survey, a survey of practitioners of traditional medicine and interviews with local residents attending an urban health centre with persistent diarrhoea. The classification is based on symptoms and perceptions of aetiology. While resulting categories convey imperatives for treatment choice, it is clear that individuals with diarrhoeal illnesses seek treatment from multiple sources. This may be because any single illness may fit more than one category, or because unrelenting ill-health engenders desperate behaviour. The cultural constructs do not fully explain treatment choice and attitudes to prevention, but could be used to improve communication regarding public health and treatment strategies.