Background:Shoe heel height is considered to influence prosthetic alignment, walking comfort, and gait symmetry in people with a transtibial amputation (TTA). However, research on the effect of heel height is scarce, and no evidence is available on the effects of variations smaller than 20 mm. These small heel height variations between store-bought shoes are often overlooked by people with an amputation and may cause secondary musculoskeletal problems in the long term.Objective:To examine the effects of small increases in heel height on gait symmetry in people with a TTA and healthy individuals.Study design:Experimental repeated measures study.Methods:Fourteen participants with a TTA and 15 healthy controls were included. Pressure data, spatiotemporal data, and experienced walking comfort were measured during walking with four heel height conditions: original height and increased heights of 3, 5, and 8 mm. Symmetry in center of pressure velocity (VCOP), gait parameters, and experienced walking comfort were compared between the heel heights and between healthy controls and prosthetic walkers.Results:Increased heel height resulted in a significant decrease in VCOP symmetry (P = 0.001) and experienced walking comfort (P < 0.001). The VCOP trajectory of the prosthetic leg mainly differed within the first 14.5% of the stance phase. Healthy individuals showed better VCOP symmetry in all conditions (P < 0.001).Conclusions:Healthcare professionals should advice their clients to be alert of small heel height differences between store-bought shoes, especially those larger than 5 mm. A prosthetic alignment adjustment should be considered when purchasing new shoes.