OBJECTIVE: The purpose of this investigation was to test a new procedure for quantifying lateral pelvic displacement during walking. DESIGN: A quasi-experimental design was used to quantify the gait of 18 unimpaired people and one person with hemiplegia. BACKGROUND: Although previous techniques provided useful information on amplitude of lateral pelvic displacement, they did not consider step-to-step variations in walking direction or enable quantification of symmetry. METHODS: Three-dimensional motion analysis was used to collect the coordinates of light-reflective markers placed on the scarum and heels of each subject. Subjects performed one 10 m overground walk at their preferred speed. Amplitude and symmetry of lateral pelvic displacement were quantified relative to the step-to-step variation in the path of motion (base of support). RESULTS: The mean amplitude of lateral pelvic displacement for the unimpaired group was 40.8 mm, and symmetry was 3.1 mm. The amplitude of lateral pelvic displacement for the hemiplegic person was 88.4 mm. Symmetry was 30.9 mm, with deviation toward the non-paretic side. CONCLUSION: The new procedure provided information on the amplitude and symmetry of lateral pelvic displacement in unimpaired adults and was sensitive to deviations of a person with a walking abnormality. RELEVANCE: Treatment of atypical lateral pelvic displacement is frequently an aim of stroke rehabilitation. Therefore, it is important to have objective, accurate methods of quantification.