The concept of "desirable" weight derives from analyses of data in which relative body weight is correlated with mortality experience. "Ideal" or lowest-risk weights vary for different populations, and vary for the same population at different times and in relation to different causes of mortality. An ideal weight cannot be identified at a point in time for a person or persons differing from the groups on which desirable-weight tables were based. This fact, plus the limitations of existing tables and databases, has prompted some observers to suggest abandoning the concept of ideal weight. The recent publication of updated data for the U.S. population and updated height-weight tables based on actuarial data have focused attention on this issue. In addition, several studies have attempted to relate body weight to mortality in defined populations. At the same time, some studies have found significant relationships between overweight and mortality whereas others have not.