The goal of this study was to characterize the expected range of variation in T1 (spin-lattice relaxation time) of brain tissue in vivo, as a function of age, and to use these maturational norms to study children with sickle cell disease (SCD). A well-validated method (TurboPAIR) was used to measure T1 in 10 tissues in a study group of 200 healthy subjects (ages 4.5 to 79.3; 101 male and 99 female), in a transverse slice at the level of the basal ganglia. Brain T1 was significantly related to age in every tissue characterized (p < 0.001), including the splenium (p < 0.01). Quantitative MRI suggests that brain T1 continues to change throughout the lifespan of healthy subjects free of neurologic complaints. Age-related changes follow a different schedule in each tissue, and age is a stronger determinant of T1 in gray matter than in white matter. Analysis of 141 patients with SCD shows that patients have lower T1 than normal, in both the caudate and the cortex (p < 0.001).