The insertion/deletion (I/D) polymorphism of the ACE gene may be involved in structural arterial changes. Aim of the present study was to assess the relationship between the ACE I/D gene and vessel wall stiffness among older adults. The study was conducted within the Rotterdam study, a population-based cohort study including subjects aged 55 years and older. The II, ID and DD genotypes of the ACE gene were determined in all subjects. The distensibility coefficient (10(-3)/kPa) of the carotid artery and the carotid-femoral pulse wave velocity were measured during the third phase of the Rotterdam study (1997-1999) and were used as measure of arterial stiffness. Data on both carotid stiffness and the ACE genotype were available for 3001 participants. After adjustment for age and gender, subjects with the ID and DD genotype had higher carotid stiffness compared to subjects with II genotype (distensibility coefficient (10(-3)/kPa) 10.24 (95% CI, 10.06-10.43), 10.27 (95% CI, 10.02-10.52), 10.65 (95% CI, 10.37-10.93), respectively (ID versus II genotype, P = 0.017), (DD versus II genotype, P = 0.037)). In stratified analyses, the association was strongest in subjects younger than 70 years. No difference was seen for pulse wave velocity among genotypes. In conclusion, the results of this population-based study show that the ACE ID/DD genotypes are associated with higher common carotid stiffness.