A multivariable statistical model for predicting the duration of life of rats permitted to select their own diets was evaluated prospectively. With information relating to pre-adult dietary habits and growth responses, the predicted length of life for an individual closely matched the observed life span; the average absolute error was 11%. This suggests that, even under normal feeding conditions, the diet/growth history is an important factor bearing on death rate. In general, an early adult death age is associated with a high food intake prior to adulthood particularly when coupled with a high efficiency of food utilization during the post-puberty period, a rapid growth rate and early attainment of mature weight. Deviations from this pattern serve to increase the duration of life of the individual.