The population approach to prevention has been described as one of the "absolute truths" of preventive medicine. However, when the relationship between risk factor exposure levels and associated risk is J-shaped the population approach can increase risk in a small number of individuals. There is evidence that the relationship between a variety of exposures and all-cause morbidity and mortality is J-shaped. However, such relationships are often overlooked by epidemiological investigations which focus on cause-specific morbidity and mortality. Although the overall beneficial effect of population interventions may outweigh any negative effect seen, the effect on the individuals concerned should not be overlooked--especially when they can be easily identifiable before the intervention. Procedures, akin to gaining informed consent in clinical situations, may be required to ensure that individuals who are at high risk of being negatively affected by population interventions understand the risks involved and have the opportunity to opt out.