Objectives To estimate the rate of unintentional drowning mortality and hospitalised morbidity using population-based, population-risk and person-time denominator data and to compare the estimates obtained. To then compare exposure-based rates for drowning with road traffic death rates.

Method Retrospective analysis of unintentional drowning mortality and hospitalised morbidity of New South Wales (NSW, Australia) residents 16+ years of age during 1 January to 31 December 2005. Information on population-risk and person-time risk was obtained from the 2005 NSW Population Health Survey. Analysis of road traffic death data from NSW and population and person-time risk estimates from the Survey of Vehicle Use, Household Travel Surveys and Roads and Traffic Authority Speed Surveys in 2005.

Results Estimated drowning mortality and hospitalised morbidity rates for adults were higher using population-risk and person-time risk exposures compared to a population-based exposure. Population-based estimates of road traffic mortality were four times higher than drowning mortality rates. In contrast, exposure adjusted person-time estimates for drowning were 200 times higher than road traffic fatalities.

Conclusions Many injury risks are underestimated when the total age-specific population is used to calculate an injury rate instead of actual population-risk or person-time exposure. This can result in the identification of misleading priorities for injury prevention. Drowning risk is strikingly higher than previously thought based on population-based estimates. This information is important for decision-making and policy development as it provides a basis for comparing the inherent risk in exposure to hazards with potential to cause injury.