Mouse lemurs (Microcebus murinus) are prosimian primates described to be convenient models of brain aging. We observed very high correlations between the T2-weighted magnetic resonance imaging (MRI) signal decrease and the natural logarithm of age in the basal ganglia. The correlation coefficient was higher for the pallidum (r = 0.95, P < 0.0001) than for other structures. We suggest that the ratio of the pallidum intensity divided by the amygdala and temporal lobe intensity should be a valuable non-invasive marker of age and of cerebral aging. It should be particularly useful for the non-invasive assessment of interventions and drugs that affect the aging process.