A 71-year-old female underwent a (99m)Tc-MIBI scan to characterize a cold nodule (30 mm) of theleft thyroid lobe. The nodule showed diffuse uptake andretention of the radiotracer. After resection, histologicalexamination demonstrated a microfollicular adenoma withdiffuse white adipose metaplasia. Although mitochondria inbrown adipose tissue have been widely studied, we have onlya limited understanding of the relevance of mitochondria inwhite adipose tissue. Active mitochondria are present in whiteadipocytes, and this may account for the MIBI uptake, mimickinga hyperproliferation pattern, in our patient.