Cerebral metabolic rate of oxygen (CMRO2) has been reported to vary as a function of age and gender. Here, we re-examined possible gender differences as part of an ongoing study in people over the age of 60 years by means whole-brain MR oximetry. Data corroborate earlier findings that cognitively normal females appear to have higher CMRO2 than their male peers. This difference may be largely due to greater oxygen extraction rather than changes in cerebral blood flow. Possible biological causes of this gender bias will need detailed scrutiny, as do the underlying physiologic assumptions that may impact the results.