Background From pathological studies of coronary arteries, it has been recognized that progressive plaque development may be compensated for by an increase of the arterial diameter. However, the dynamics of this process have not been investigated, and it is not known whether compensatory dilatation is a general pathomechanism in human arteries.Methods and Results Using a high-resolution duplex scanner and subsequent three-dimensional plaque reconstruction, we prospectively studied the effect of carotid plaque development on the vascular geometry in 32 patients at 6- to 12-month intervals. Plaque progression in 41% (n=26) of studies was associated with an increase of the vessel diameter between 0.4 and 1.2 mm in 76% (n=20). Among 36 unchanged plaque developments, enlargement of the arterial diameter was assessed in only 28% (n=10) (P<.001).Conclusions Our data suggest that increasing plaque volume is significantly associated with enlargement of carotid artery segments, which compensates for arterial narrowing in early stages of the disease. (Circulation. 1994;89:2578-2581.)