Purpose: To analyze epidemiological and anthropometric features of patients with brown adipose tissue (BAT) activation detected by fluorine18-fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F-FDG PET/CT)., Material and Methods: From 2005 to 2017, 818 18 F-FDG PET/CT studies positive for BAT detection were retrospectively included, 742 examinations performed on the adult population and 76 PET/CT on the pediatric population. A Chi-squared test was performed to compare features distribution between the adult and pediatric patients., Results: Adults showed a higher rate of BAT detection in females (79% vs. 61%, P<0.001) and in hyperglycaemic patients (>100mg/dL) (24% vs. 16%, P=0.02), no significant difference was found with regard to overweight patients (BMI>25kg/m 2 ) (22% vs. 20%, P=.55). Considering females only, the adults showed a higher rate of BAT detection both in hyperglycaemic (83% vs. 42%, P<0.001) and overweight patients (80% vs. 67%, P=0.005). In both populations BAT activation happened more frequently in cold seasons; there was no significant distribution difference with regard to season of birth (P=0.2)., Conclusions: Sex, glycemia and BMI play a major role in predicting BAT activation, with significant differences between adults and pediatric patients. Cold exposure is confirmed as an important predicting factor, while season of birth is not significant., (Copyright © 2019 Sociedad Española de Medicina Nuclear e Imagen Molecular. Publicado por Elsevier España, S.L.U. All rights reserved.)