The aim of the study was to assess short- and long-term reliability of the harmonic analysis of the trajectories of head, upper trunk, and pelvis during walking in healthy older women, which reveals mechanisms to coordinate upper body segments and control head stability in the search for a safer gait. A stereophotogrammetric system was used to measure the displacement of markers located at head, shoulder, and pelvis level in 11 healthy older women (77+/-2 years) walking on an oval shaped 20-m walkway circuit, in three experimental sessions separated by 6 weeks. The harmonic analysis of the time-curves was highly reliable both within and between sessions (standard error of measurement ranging between 0.15 mm and 1.50mm for the amplitudes and 0.03 rad and 0.41 rad for the phases) and revealed different oscillatory patterns for the pelvis, head, and upper trunk. An intrinsic pattern, representing the natural overall movement symmetry of the whole population of older women of this study, was described by the first medio-lateral harmonic and second antero-posterior and vertical harmonics. An extrinsic pattern, characteristic of each individual in the population, was described by the first antero-posterior and vertical harmonics. The intrinsic pattern was both intra- and inter-subject repeatable (coefficient of multiple correlation, CMC, ranging between 0.82 and 0.99), while the extrinsic pattern was only intra-subject repeatable (CMC ranging between 0.70 and 0.90). Harmonic analysis reliably describes upper body kinematics in older women for detecting the intrinsic and extrinsic patterns of gait, which reveal fundamental mechanisms governing their walking.