AbstractAs shown in 744 adult men and women aged 30–49 at entry and followed for 21.4 ± 0.9 years there is continuing subperiosteal expansion in both sexes as well as continuing and increasing endosteal surface resorption. In this longitudinal study, bone loss (as shown by medullary cavity expansion) begins by the 5th decade and increases thereafter. The smaller gains at the outer bone surface are essentially independent of the larger losses at the inner (endosteal) surface and neither functionally nor causally related. Though bone loss and net bone loss is nearly as great in men as in women, absolutely speaking, two‐decade bone loss constitutes a larger percentage of the initially smaller bone mass in the female. In both sexes subperiosteal apposition (delta TA) and endosteal resorption (delta MA) are bone‐size dependent though in diametrically opposite directions. These trends in two‐decade bone change are not affected by smoking behavior, alcoholic beverage usage, antihypertensive usage, or early menopausal age. Similarly, the long‐term bone changes prove to be independent of energy and mineral intakes and to long‐term changes in calcium, phosphorus, magnesium, and vitamin D intake. Though dietary intakes do not predict long‐term bone changes, the amount of tissue bone present at entry is highly correlated (>0.93) with tissue bone 21.4 years later in men and women alike. Accordingly, only a small amount of intraindividual cortical variance in the later years still remains to be explained by life‐style, dietary, medication, and