The objective of this study was to assess the effects of prolonged cafeteria-diet feeding on tissue composition in adult rats comparing those that had been overfed in early life and then in adulthood with a group that was only overfed in adulthood, and to determine whether any alterations were related to the high energy diet per se or to obesity. In addition to following the body weight changes in detail, tissue masses and composition were determined at selected points of this long term dietary experiment. The marked changes in body weight and tissue composition of cafeteria-fed obese rats were sustained for at least 84 days after returning to the standard diet, and the obesity was exaggerated if these animals were pre-exposed to the palatable diet in early life. Three patterns of tissue composition in response to cafeteria feeding could be discerned: Liver and brown adipose tissue developed cell hypertrophy without apparent hyperplasia. In contrast, the retroperitoneal white adipose depot developed hyperplasia whereas the intestine and kidneys were not associated with marked changes in lipid composition. These adaptations were not recovered to control levels by prolonged standard diet feeding. Previous obesity influenced the adaptations in adipose tissue during the subsequent return to standard diet feeding, and differences between cafeteria-induced obese animals became more apparent when the cafeteria diet was removed. These results indicated the important effects of early dietary experience in subsequent responses to overfeeding.