Aim: Manipulation of human brown adipose tissue (BAT) represents a novel therapeutic option for type 2 diabetes mellitus and obesity. The aim of our study was to develop and test a novel Magnetic Resonance Imaging (MR) based method to identify human BAT and delineate it from white adipose tissue (WAT), and validate it by providing histological and immunohistochemical confirmation of BAT. Methods: Initial scanning with 18F-FDG PET-CT radiotracer uptake on a 25-year old Caucasian female with primary hyperparathyroidism, showed avid uptake within the mediastinum, neck, supraclavicular fossae and axillae, consistent with BAT. Subsequently, serial MR scans were performed using 3-echo IDEAL (iterative decomposition of water and fat with echo asymmetry and least-squares estimation) sequence. Retrospectively, regions of interest (ROIs) were identified on MR corresponding to PET-CT images. Prospectively, ROIs were identified on MR images based on signal intensity and appearance, and compared with PET-CT. Immunohistochemical staining using uncoupling protein-1 antibody was performed on fat samples corresponding to low MR-signal, obtained during parathyroidectomy. Results: Of the 111 retrospectively identified ROIs from PET-CT scans, 88 (79%) showed corresponding low signal on the MR images: 100% in mediastinum, 29/31 (93.5%) in neck, 31/41 (75.6%) supraclavicular, and 8/14 (57%) in axillae. Prospectively, 87% of ROIs identified on MR scans corresponded to increased areas of uptake on PET-CT scans. Histology and immunohistochemistry confirmed BAT. Conclusion: We provide the first ever report that MR can be used reliably to identify BAT in a human adult, with histological and immunohistochemical confirmation. Our data demonstrate proof of concept to support the development of MR, a safe and reproducible imaging modality, as a biomarker for human BAT.