Background: We examined the relationship between the intima-media thickness of the common carotid artery (CCA-IMT) and arterial stiffness, assessed by pulse wave velocity (PWV), the ambulatory arterial stiffness index (AASI) and the augmentation index (AIx) in subjects with and without type 2 diabetes.Methods: A case-series study was made in 366 patients (105 diabetics and 261-non-diabetics). Ambulatory blood pressure monitoring was performed on a day of standard activity with the SpaceLabs 90207 system. AASI was calculated as "1-slope" from the within-person regression of diastolic-on-systolic ambulatory blood pressure readings. PWV and AIx were measured with the SphygmoCor system, and a Sonosite Micromax ultrasound unit was used for automatic measurements of CCA-IMT.Results: PWV, AASI and CCA-IMT were found to be greater in diabetic patients, while no differences in AIx were observed between the two groups. CCA-IMT was independently correlated to the three measures of arterial stiffness in both groups. We found an increase in CCA-IMT of 0.40, 0.24 and 0.36 mm in diabetics, and of 0.48, 0.17 and 0.55 mm in non-diabetics for each unit increase in AASI, AIx and PWV. The variability of CCA-IMT was explained mainly by AASI, AIx and gender in diabetic patients, and by age, gender, AASI and PWV in non-diabetic patients.Conclusions: CCA-IMT showed a positive correlation to PWV, AASI and AIx in subjects with and without type 2 diabetes. However, when adjusting for age, gender and heart rate, the association to PWV was lost in diabetic patients, in the same way as the association to Alx in non-diabetic patients. The present study demonstrates that the three measures taken to assess arterial stiffness in clinical practice are not interchangeable, nor do they behave equally in all subjects. © 2011 Gómez-Marcos et al; licensee BioMed Central Ltd.