An understanding concerning the roles of the various degrees of freedom of the human body during functions such as walking is crucial to the design of robotic devices for rehabilitation. However, the function of the three rotational degrees of freedom of the pelvis during walking remains uncertain. Theories have been previously presented postulating a role of pelvic obliquity in reducing vertical movements of the body's centre of mass, and therefore in minimising energy expenditure, but these are not fully supported by empirical evidence. In this paper, an alterative role of pelvic obliquity in reducing lateral movements of the upper body is proposed. Through the application of a robotic orthosis platform, a variety of walking conditions are tested with different levels of pelvic rotation and lateral movement of the upper body. The presence of the robotic device significantly reduces the degree of pelvic obliquity. Though the data show no significant relationship between the pelvic angles and lateral movement, a trend for decreasing upper body movement with increasing pelvic obliquity is apparent.