The manner and rate of progression of atherosclerosis was evaluated in 60 patients (99 limbs) with occlusive disease and 18 patients (36 limbs) with abdominal aortic aneurysms. The measurement of seg-mental limb pressure gradients was utilized in evaluating disease progression. Progression of disease during the average 3-year follow-up occurred in 34 (43%) of the limbs that had occlusive disease at the outset. When patients rather than limbs are considered, 31 (52%) had progression of disease. Of the 31 patients, 12 were unaware progression had occurred. Of 19 limbs without occlusion at the outset of the study, 9 developed a major artery obstruction. Ten of the 12 patients with diabetes mellitus exhibited progression of disease. Four of the 18 patients with abdominal aortic aneurysm had coexisting arterial obstruction with disease progression occurring in 6 patients.