Extensive experimental investigations were conducted on the Vincent-Thomas Suspension Bridge at Los Angeles Harbor to determine natural frequencies and mode shapes of vertical, torsional, and lateral vibrations of the structure. These ambient vibration tests involved the simultaneous measurements of both vertical and lateral vibrational motions caused by traffic. Measurements were made at selected points and different cross sections of the stiffening structure. Comparison with previously computed mode shapes and frequencies showed good agreement with the experimental results, thus, confirming both the accuracy of the experimental determination and the reliability of the method of computation.