Arterioles of the human retinal circulation are directly visible and exhibit wide variations in their course. Not only is there marked variation in arteriolar tortuosity within a given age group, but also it has been proposed that the degree of arteriolar tortuosity is different in younger and older age groups. This paper reports on the development of a computer-assisted technique for measurement of arteriolar tortuosity and on the frequency distribution of this index in younger (mean age 22 years) and older (mean age 54.3 years) populations without hypertension.