The worst flood in the history of Bangladesh affected millions of people in 1988. To determine morbidity and mortality during the flood, we investigated the causes of illness in 46,740 patients and causes of death in 154 persons while providing medical relief services in 72 flood affected upazilas (sub-districts). Diarrhoea was the most common illness (34.7%), followed by respiratory tract infections (17.4%). Watery diarrhoea was the most common type (47%) of diarrhoea and the most common cause of death for all age groups except those above 45-years of age. Respiratory disease was responsible for 13% of all reported deaths; only 7% of these were associated with acute respiratory tract infections. Accidental deaths accounted for 9.7% of the reported deaths: 5.8% of those were due to drowning, a figure twice as high as that reported previously. Our study suggests that floods have influenced the distribution of disease and death among the affected population.