AbstractThis study explores changes with age in the medullary cavity in an area of the femur which is becoming of increasing clinical interest. It is based on measurements of medial‐lateral and posterior‐anterior radiographs of the proximal one‐third of the right femur, below the greater trochanter. The study population consisted of 257 individuals from the Terry collection in the Smithsonian Institution and included Blacks and Whites, males and females, aged 20 to 90 years. Medullary cavity and external diameters were measured at 11 levels, beginning with a line drawn perpendicular to the linea aspera at the level of the inferior border of the greater trochanter. To correct for size differences, the interval between levels was set at one‐fourth the individual femoral head diameter. The data were subjected to regression analysis and analysis of variance.Anterior‐posterior medullary diameter is more highly correlated with age than medial‐lateral diameter. Females show the greatest relative increase with age in both dimensions, especially at subtrochanteric levels, and they tend to have relatively larger medullary cavities than males at all ages. White males have relatively larger medullary diameters than Black males. Younger White females have relatively larger medullary cavities than Black females, but the latter reach parity with White females in middle age and show a greater overall percentage of medullary expansion.