Human brown adipose tissue (BAT) has recently found to be functionally active in adults. The purpose of this review is to chart the importance of BAT in the light of recent publications in humans.After publication of the direct evidence of functional BAT in human adults the original findings in human studies have been sparse. This indicates that intensive human data collection is ongoing.Brown adipocytes and myocytes share the same origin. Regardless of different origin, brown and white adipocytes transdifferentiate into each other's under specific exposure but in addition, another cell type is suggested to exist, 'brite' adipocyte, holding the capacity of transdifferentiation. This indicates the plasticity of adipose organ.Human BAT can be detected using PET. Cold exposure increases the probability to detect brown fat due to increased metabolic activity by induced thermogenesis.BAT glucose uptake rate is 10-15-fold higher in cold than in normal room temperature. Other factors that may increase the activity of sympathetic nervous system and uncoupling protein 1 are several including the complex network of hormonal and neuronal signals. Preliminary results suggest that BAT resembles skeletal muscle not only by origin but also by the effect of insulin on the tissue.