Degeneration of the coracoacromial ligament (CAL), which is related to age, may cause it to become stiff. The objective of this study was to compare the difference in CAL displacement during shoulder motion between different age groups by dynamic ultrasonographic examination. Thirty aged (> 55 years old) and 26 young (< 35 years old) healthy persons without shoulder pain participated in this study. In a static examination, the length and thickness of the CAL and the shortest distance between the CAL and the humeral head were measured. During the dynamic examination, the CAL displacement was filmed, and both active and passive shoulder motions (shoulder abduction and internal rotation, SAIR) were recorded. The CAL displacement was reviewed and measured until the maximal displacement was recorded. The Mann-Whitney U test was used to compare the demographic data and the ultrasonographic parameters between the aged group and the young group. During the passive SAIR motion, CAL displacement of the aged group was significantly smaller than that of the young group (median = 1.75 mm, interquartile [IQ] range, 1.31-2.26 mm vs. median = 2.20 mm, IQ range, 1.33-3.02 mm; p = 0.003). The same difference was noted during active SAIR motion (median = 1.90 mm, IQ range, 1.38-2.41 mm vs. median = 2.35 mm, IQ range, 1.61-2.92 mm; p = 0.001). However, with the static examination, there were no differences in CAL thickness, CAL length, and the shortest distance between the CAL and the humeral head between the two groups. Using dynamic ultrasonography, displacement of CAL was smaller in aged participants compared with that in young participants. © 2010 Chinese Taipei Society of Ultrasound in Medicine & Elsevier.