Large White toms were used in an experiment to determine the response of turkeys to feeding supplemental fat by age sequence. The eight treatments tested consisted of a factorial arrangement of dietary animal-vegetable fat blend (A-V fat) at 0 and 4% and four age periods (0 to 20, 6 to 20, 9 to 20, and 12 to 20 weeks). The concentrations of nutrients were kept constant within an age period, irrespective of level of dietary fat. On an age-period basis, improvements in feed efficiency resulting from supplemental fat increased with increasing age. During the 0- to 6-week period, feed efficiency was improved 1.6% per 1% added fat, while during the 12- to 20-week period, feed efficiency of toms previously fed no added fat was improved 3.6% for 1% added fat. Improvements in weight gains through 12 weeks of age followed a similar pattern but of lesser magnitude. The overall data through 20 weeks of age demonstrated that nearly all of the increases in weight gain and much of the improvements in feed efficiency obtained by feeding supplemental fat from 0 to 6, 0 to 9, and 0 to 12 weeks of age were lost after these treatment groups were fed a diet with no added fat for the rest of the growing period. Conversely, 20-week feed efficiencies and efficiencies of metabolizable energy and protein utilization were similar for all treatment groups that received no supplemental fat from 0 to 6, 0 to 9, or 0 to 12 weeks of age but were then fed 4% supplemental fat thereafter. A small numerical advantage in 20-week body weights was observed for toms fed supplemental fat from 0 or 6 to 20 weeks of age as compared with those fed fat-supplemented diets from 9 or 12 to 20 weeks of age.