Findings show that proximal femur diaphyseal shape can be used to distinguish between platymeric Native American femora and more eurymeric American Black/White femora in subadults over the age of 6 years with as much as 85 percent accuracy by using the Gilbert and Gill and discriminant function methods. At birth, the proximal femur diaphysis is relatively circular in both Native Americans and American Blacks/Whites. Between birth and 5 years old, the diaphysis becomes more mediolaterally broad, especially in Native Americans, due to differential growth between the mediolateral and anteroposterior planes. After 5 years old, growth occurs more equally in the two planes, and shape does not change significantly. The adult shape of the proximal femur is established by approximately 5 years old and can be used to distinguish between Native American and American Black/White femora in older subadults. Subadults, like adults, show significant variation within racial groups, probably due to activity-induced biomechanical stress placed on the femur and environmentally influenced temporal changes. This variation should be taken into account when using femur subtrochanteric shape alone to determine ancestry in medicolegal investigations. The study involved 74 Native-American and 61 American Black/White subadult femora. 6 figures, 2 tables, and 31 references