The visualization of hypermetabolic brown adipose tissue (BAT) on 18F FDG PET lowers the efficacy of PET and has been linked with the environmental temperature of the patient before presentation. The objective of this paper is to investigate the effectiveness of thermal control on BAT and 18F-FDG PET. Methods: Three hundred patients undergoing 18F-FDG PET were defined by 1 of 2 groups. Group A consisted of 150 consecutive patients from August to October 2009 (spring). Group B consisted of 150 consecutive patients from December to February 2010 (summer). In addition to normal preparation, group B received instructions to dress warmly and was warmed during the uptake period of their scan. Images were assessed for the presence of BAT. Standardized uptake value data were collected and compared. Results: BAT was present in 9.3% of patients; 15.3% of patients that were not warmed (group A) demonstrated BAT, and this was reduced to 3.3% in the group that underwent warming (group B) (P = 0.0005). BAT was more common in men (10.9%) than women (6.8%), and women responded better to warming. Younger patients were more likely to demonstrate BAT (P < 0.001). No significant relationship between BAT and height, weight, or body mass index was found. The most common site for BAT visualization was the cervical region (89%), followed by supraclavicular (75%), paravertebral (50%), suprarenal (21%) and paraaortic (7%) regions. Conclusion: Thermal control for the reduction of BAT can achieve reductions in the incidence of BAT by as much as 78%. The reduction of BAT on PET images can reduce false-positive and false-negative results and minimize the need for rescanning.