Population, the most often used denominator in calculating drowning mortality rate, might not be a good measure of risk exposure. In this study, we sought to compare the rankings of township drowning mortality according to population-based rates with those according to aquatic area-based rates in Taitung County, Taiwan. The township with the highest mortality rate using population as the denominator (deaths per 100 000 persons) was Changbin (32.3) followed by Lanyu (22.4), Donghe (19.6) and Chenggong (18.0). On the other hand, the township with the leading mortality rate using aquatic area as the denominator (deaths per 100 000 km2) was Lanyu (353) followed by Lyudao (307), Chenggong (282) and Taitung City (219). Taitung City ranked 10th according to the population-based rate, but ranked 4th according to the aquatic area-based rate. In conclusion, rankings of regional drowning mortality rates using aquatic area as the denominator differ from those using population as the denominator.