Lesotho is experiencing a problem of seasonal bloody diarrhoea outbreaks that occur in the southern districts of the country. Usually large proportions of the meagre resources are used to combat such outbreaks. Measures have been taken to provide water and improve sanitation for the commonly affected communities. However, the problem has continued unabated. There was therefore, a need to isolate factors that are associated with the transmission of bloody diarrhoea among the communities in the Moriti, Holy Cross, Liphiring and Mohalinyane health centres where bloody diarrhoea is prevalent. In this study, 145 cases of bloody diarrhoea and 269 controls were selected from the four health centres. Cases and controls were selected from subjects who were seen in the health centres during the period of December 2002 to February 2003. All available cases were selected whereas controls were selected by systematic sampling. The study examined environmental factors such as water source, waste and refuse disposal and hygiene practices. Binary logistic regression was used to estimate the effects of several exposures on bloody diarrhoea. The model showed maintenance of the boreholes to be the most important variable. The Odds ratio among people who experienced unavailability of water was 3.88 greater, among children who do not wash hands the odds ratio was 4.66 higher. Among subjects who ate bread in January the Odds ratio was 1.45 more and among subjects who had someone with bloody diarrhoea in the household the Odds ratio was 2.60 greater.