This magnetic resonance (MR) imaging study analyzed and provides normative data on the midsagittal surface area of the corpus callosum (CC) across the human adult life span in 200 normal volunteers. Using MR imaging scans, CC midsagittal surface area was quantified, along with midsagittal intracranial surface area and total intracranial volume (measures of cranial size). Results demonstrate that when head size is controlled, no major changes associated with normal aging are evident in the CC during the more active years of adult life span (up through 65). Overall, females had significantly larger CC relative to total intracranial volume. Results are discussed in terms of potential gender differences in CC size and the clinical application of this normative data.