Calcification of the aorta is characteristic of artherosclerotic disease. A novel numerical index for quantitating the extent of calcification observed in computed tomography (CT) scans has been developed. The index weights the fractional area of the aorta showing calcifications with the average calcium density in the plaques. It obviates the need for manual tracing of the calcifications, and avoids the arbitrary nature and lack of reproducibility of the ''calcium score'' system currently used in assessing CT scans. Continuously different levels of calcification were distinguished in the abdominal aortas of a group of Kuwaiti females (n = 20), with a linear correlation coefficient between index value and age of 0.914 (P < 0.0001) over three decades. The index is generally applicable to all arterial calcifications, and could be used to monitor the effect of therapeutic regimes. It could easily be modified for use with 3D reconstructions obtained from CT helical scanning or MRT. (C) 1997 Elsevier Science Ltd.