The goal of this study was to determine the expected normal range of variation in spin-lattice relaxation time (T1) of brain tissue in vivo, as a function of age. A previously validated precise and accurate inversion recovery method was used to map T1 transversely, at the level of the basal ganglia, in a study population of 115 healthy subjects (ages 4 to 72; 57 male and 58 female). Least-squares regression analysis shows that T1 varied as a function of age in pulvinar nucleus (R2 = 56%), anterior thalamus (R2 = 51%), caudate (R2 = 50%), frontal white matter (R2 = 47%), optic radiation (R2 = 39%), putamen (R2 = 36%), genu (R2 = 22%), occipital white matter (R2 = 20%) (all p < 0.0001), and cortical gray matter (R2 = 53%) (p < 0.001). There were no significant differences in T1 between men and women. T1 declines throughout adolescence and early adulthood, to achieve a minimum value in the fourth to sixth decade of life, then T1 begins to increase. Quantitative magnetic resonance imaging provides evidence that brain tissue continues to change throughout the lifespan among healthy subjects with no neurologic deficits. Age-related changes follow a strikingly different schedule in different brain tissues; white matter tracts tend to reach a minimum T1 value, and to increase again, sooner than do gray matter tracts. Such normative data may prove useful for the early detection of brain pathology in patients.