Ultrasound measurement of wall thickness of the carotid artery is used in large cardiovascular clinical trials and epidemiologic studies. Improvements in measurement reproducibility could have important implications for study design and sample size calculations. This study examined the effects of B-mode color on the validity and reproducibility of measurements of far wall thickness of the common carotid artery. Six color maps were compared with normal and inverted gray scales. The validity of B-mode color was assessed by comparing histologic measurements from 20 excised human common carotid arteries with measurements made using each map. No differences were noted in the average far wall thickness measured by any method (all p > 0.99). The reproducibility of duplicate measurements was assessed using each of the B-mode color maps. The coefficient of variation between the two measurements ranged from 6.7% to 9.7%. These variations were not significantly different between each map or gray scale (p > 0.24). In conclusion, B-mode color maps do not distort ultrasound measurements of far wall thickness of the common carotid artery. The reproducibility of these measurements is neither significantly nor usefully improved by using different color maps. Because no additional information is obtained, the use of color may not be warranted.