The potential life loss caused by floods has not been studied before. We carried out a retrospective cohort study in flood areas in Hunan, China in 1999. The standard mortality rate (SMR) and years of potential life lost (YPLL) were used to quantify the burden of flood on health. The SMRs of injury/poisoning and malignant neoplasm were higher in the river flood (151.36 x 10(-5), 127.30 x 10(-5)) and drainage problems (143.74 x 10(-5), 105.87 x 10(-5)) groups than those in the no-flood group (113.40 x 10(-5), 74.81 x 10(-5)). The standard rates of YPLL (SYPLL per thousand) in the river flood (89.56 per thousand) and drainage problems (71.30 per thousand) groups were significantly higher than those in the no-flood group (65.74 per thousand, P<0.05). The SYPLL was significantly higher in males than in females. The percentages of attributable risk (PARs) of SMRs and PARs of SYPLLs resulting from flood were 12.26 and 26.60% in the river flood group and 10.56 and 7.80% in the drainage problems group. We conclude that floods increase the affected residents' SYPLL, and that the river flood had stronger effects than the drainage problems floods.