The question of an age-associated rise in serum cholesterol has been undecided. This communication presents evidence in favor of a rise in serum cholesterol with increasing age between the third and the fifth decades. In a control group of 146 individuals and a coronary disease group of 97 individuals, there was a positive correlation between age and serum cholesterol. In the coronary disease group, there was a rise in serum cholesterol superimposed upon an initially higher level of serum cholesterol. The concept of "cholesterol age" is presented on the basis that a patient with coronary heart disease at 25 has a serum cholesterol similar to a "normal" male at the age of 45. The role of serum phospholipids is considered in the age-associated rise in serum cholesterol.