Brown adipose tissue (BAT) functions as a thermogenic organ by producing heat to maintain body temperature in many mammals, especially in the young. BAT is generally found in deep cervical, supraclavicular, interscapular, and paravertebral regions, as well as areas near large vessels. If not recognized, BAT activity can considerably interfere with 18F-fluorodeoxyglucose position emission tomography (PET)/computed tomography (CT) image interpretation. BAT activation can be influenced by several factors and reduced by different methods. In this paper, we review BAT distribution and factors influencing BAT activity on FDG PET/CT scan. The purpose of this review is to enhance the recognition of pediatric-related physician of BAT on FDG PET/CT scan.