Extensive literature documents age-related differences in spatiotemporal variables during gait. Recent efforts have focused on upper body control and balance during gait. Harmonic ratios, derived from trunk acceleration signals, measure smoothness of motion, and are an indication of dynamic balance during gait. Limited and conflicting information exists regarding the effect of walking speed on harmonic ratios, as well as age-related differences. This research extends previous literature by: 1) examining harmonic ratios across a range of self-selected speeds in young adults; 2) comparing harmonic ratios at preferred speed in young adults, healthy 60-year-olds, and healthy 80-year-olds; and 3) comparing harmonic ratios in all three age groups across a range of self-selected and paced speeds. In contrast to previous research, young adults and 60-year-olds had similar trunk smoothness during over ground walking at a preferred pace, but 80-year-olds exhibited reduced smoothness specifically in the anteroposterior direction. In contrast to previous research, clear optimization of trunk smoothness at preferred speed in young adults was not found; trunk smoothness was reduced at slower speeds, but was maintained at speeds faster than preferred. The two older groups showed this same pattern, although the 80-year-olds exhibited reduced anteroposterior and vertical smoothness across speeds. Together, these findings indicate that active healthy 80-year-olds exhibit changes in trunk control even during unobstructed walking at their preferred pace. But contrary to expectations, changes in speed did not differentially affect 80-year-olds, except at very fast walking speeds