Positron emission tomography (PET) combined with computed tomography (CT) is used to detect brown adipose tissue (BAT) in humans. Function can be measured using different tracers, most typically with glucose analog 18F-fluoro-deoxyglucose (FDG). CT provides an anatomical reference, but this tool can be utilized for other purposes as well, such as indirect estimate of triglyceride content of the BAT. PET/CT measurements require sophisticated and highly specified devices, and manufacturer-dependent differences exist between different scanners. Therefore, complete device-specific instructions are not given in this article, but rather general guidelines which are important when human BAT is imaged using PET/CT.