We reviewed the clinical and epidemiological features of 390 children under 5 years of age infected with either Shigella dysenteriae type I or Shigella flexneri attending a diarrhoea treatment centre from 1993 to 1995 in Dhaka, Bangladesh. Older age (24 months or more), underweight and wasting but not stunting were the host factors significantly more associated with Shigella dysenteriae type I infection than in Shigella flexneri-infected children. Moreover, use of antibiotics at home, use of water from tubewells or pipe-water for drinking and lack of sanitary facilities for defaecation were the behavioural and environmental factors strongly associated with S. dysenteriae type I infection. Children with diarrhoea due to S. flexneri presented with more watery/liquid stools and had a shorter duration of illness. Duration of diarrhoea for 4 or more days was typical of S. dysenteriae type I infection. Interventions to address malnutrition and to promote environmental hygiene would be predicted to offer greater protection against shigellosis due to S. dysenteriae than S. flexneri.