<i>Aim:</i> To define reference values for mean common carotid artery intima-media thickness (CCAIMT_mean) from subjects without conventional cardiovascular risk factors. <i>Methods:</i> This nationwide study involved cardiologists at 246 centres in France. A total of 5,433 subjects with and without conventional cardiovascular risk factors participated. <i>Results:</i> In subjects without risk factors, CCAIMT_mean was 0.712 ± 0.122 mm in men and 0.682 ± 0.105 mm in women (p < 0.0001). Age explained 27.7% (men) and 33.9% (women) of the variance in CCAIMT_mean. Each 10-year increment in age was associated with a sex-adjusted increase in CCAIMT_mean of 0.049 mm. In subjects with 1 risk factor, CCAIMT_mean was 0.765 ± 0.121 (p < 0.0001 vs. subjects without risk factors). CCAIMT_mean increased continuously with increasing number of risk factors, irrespective of age group. In multivariable analysis, age, sex and number of cardiovascular risk factors appeared independently associated with CCAIMT_mean. <i>Conclusion:</i> CCAIMT_mean may help to identify the population at intermediate cardiovascular risk. As an integrator of both conventional and genetic cardiovascular risk factors at the individual level, its additive value versus other risk scores must be evaluated, particularly in patients in their fourth and sixth decades.