[Purpose] Tri-axial accelerometers have advantages, including portability, in clinical gait analysis. However, the gait parameters calculated by accelerometers cannot be used visualize the symmetry of trunk movement. The purposes of this study were to visualize the acceleration signals of the trunk during gait and to assess the usefulness of a new gait symmetry parameter derived from Lissajous figures of acceleration of the trunk. [Subjects and Methods] Trunk accelerations of 38 healthy young and 38 healthy elderly subjects were measured with a tri-axial accelerometer while walking at their preferred speed. Gait parameters assessed included: the symmetry index of the Lissajous figure (Lissajous Index; LI), and the root mean square (RMS) and harmonic ratio (HR) of the acceleration signals. [Results] Walking speed did not significantly differ between the two groups. However, LI was significantly higher, indicating less symmetry of motion, in the elderly subjects (young: 23.0%, elderly: 35.4%). RMS of the acceleration signals in the vertical and mediolateral directions were also significantly higher in the elderly subjects. [Conclusion] These results suggest that the LI may be useful for the evaluation of trunk movement in the frontal plane during gait analysis.