Purpose: Near-infrared spectroscopy (NIRS) has recently been proposed as an indirect technique to assess brown adipose tissue (BAT) in young men. NIRS arises as a novel technique to avoid the limitations of the “gold-standard” 2-deoxy-2-[18F]fluoro-D-glucose ([18F]DG) positron emission tomography combined with X-ray computed tomography (PET/CT). The aim of this study was to examine the association between near-infrared spatially resolved spectroscopy (NIRSRS) parameters and BAT volume and activity estimated by [18F]DG-PET/CT in 18 young healthy women. Procedures: NIRSRS parameters [tissue saturation index and concentrations of total haemoglobin, oxy-haemoglobin, and deoxy-haemoglobin] were continuously measured in the supraclavicular and forearm regions, in both warm and cold (2 h of personalised cold exposure) conditions. Then, the NIRSRS data were analysed as an average of 5 min in 4 different periods: (i) warm period as the baseline record, (ii) cold period I, (iii) cold period II, and (iv) cold period III. The data were then correlated with BAT volume and activity (SUVmean and SUVpeak) estimated by [18F]DG-PET/CT. Results: There was no association between the NIRSRS parameters in the supraclavicular region in warm conditions (no previous cold exposure) and BAT volume and activity (P > 0.05). Similarly, the cold-induced changes of the NIRSRS parameters in the supraclavicular region were not associated with BAT volume and activity (P > 0.05). Conclusions: NIRSRS does not seem to be a valid technique to indirectly assess BAT in young healthy women. Further research is needed to validate this technique against other methods such as PET/CT using different radiotracers or magnetic resonance imaging.