BOLD functional MRI (fMRI) for presurgical planning allows maximal brain tumor surgical resection with preservation of cortical areas critical for sensory and cognitive function. This technique can thus help to dramatically extend survival while maintaining good quality of life in these patients. Primary gliomas can alter the relationship between neuronal metabolic activity and vascular response which is the basis of BOLD fMRI. This phenomenon, reported as neurovascular uncoupling (NVU), may result in false-negative or abnormally reduced activation potentially leading neurosurgeons to remove cortical regions erroneously deemed as non-eloquent. Breath-hold cerebrovascular reactivity (BH CVR) mapping can provide a clinically viable and reliable method to assess NVU potential in both low- and high-grade gliomas. In this chapter, we will first explain BH CVR methodology, both in terms of acquisition and analysis. Then we will show how BH CVR can help in assessing NVU potential that can adversely affect interpretation of both task-based activation and resting-state functional connectivity maps. Finally, we will briefly mention alternative resting-state fMRI-based methods of NVU detection. BH CVR mapping represents an essential quality control tool that should be routinely used in clinical fMRI of primary gliomas.