Aging has been indicated as one of the major risk factors for development of atherosclerotic lesions, although the role aging plays, lacks accurate evaluation. Our study was aimed at quantitatively defining such a role by using morphometric analysis. Aged (median age 3 years and 8 months) and young (4 months) white New Zealand rabbits received a hyperlipemic diet enriched with a low dose of cholesterol for 16 months. At regular intervals, levels of serum lipemic parameters were checked. A Quantimet 920 image analyzer was used on paraffin-embedded sections of the entire aortas to measure the volume density of the tunica intima, the volume density of atheroma, the ratio intima/media and the surface area of the tunica intima. Our results indicated for aged hyperlipemic rabbits a statistically significant increase in all morphometric parameters examined as compared to young hyperlipemic animals, and no statistically significant differences in serum cholesterol, triglycerides and phospholipids.