Thoracic aortic calcium (TAC) has been associated with a higher prevalence of coronary arterial calcium (CAC). The purpose of this study was to assess the relations between TAC and incident CAC and CAC progression in a cohort from the Multi-Ethnic Study of Atherosclerosis (MESA). MESA is a prospective cohort study of 6,814 participants free of clinical cardiovascular disease at entry who underwent noncontrast cardiac computed tomographic scanning at baseline examination and at a 2-year follow-up assessment. The independent associations between TAC and incident CAC in those without CAC at baseline and between TAC and CAC progression in those with CAC at baseline were investigated. The final study population consisted of 5,755 subjects (84%; mean age 62 +/- 10 years, 48% men) who had follow-up CAC scores an average of 2.4 years later. Incident CAC was significantly higher in those with TAC compared with those without TAC at baseline (11 per 100 patient-years vs 6 per 100 patient-years). Similarly, TAC was associated with a higher CAC change (p <0.0001) in those with some CAC at baseline. In analysis adjusted for demographics and follow-up duration, TAC was associated with incident CAC (relative risk 1.72, p <0.0001) as well as with a greater CAC change (first quartile: relative risk 2.89, 95% confidence interval -3.16 to 8.95; fourth quartile: relative risk 24.21, 95% confidence interval 18.25 to 30.18). In conclusion, TAC is associated with the incidence and progression of CAC. The detection of TAC may improve risk stratification efforts. Future clinical outcomes studies are needed to support such an approach.