The pattern of adipose tissue development in humans is not well known, although it has been characterized under various conditions in rodents. In both humans and rodents there are normal periods of development characterized by marked hyperplasia. The flexibility of adipose tissue development seems to depend on the interaction of environmental and genetic factors. Because the precursor adipoblast cannot be clearly identified with a cell-specific protein, the exact mechanisms whereby adipose tissue development is regulated is poorly understood. Nonetheless, data show that various hormones and other influences modulate the normal and abnormal course of adipose tissue development.