An understanding of adverse incidents and injuries sustained by active wheelchair riders, who live and work in the mainstream of society, is needed to improve safety via wheelchair design, selection, and configuration. We interviewed 109 riders who had experienced incidents, in order to identify the causes of incidents and injuries they suffered. Participants reported n = 253 incidents (53% in powered wheelchairs, 47% manual) occurring within a 5-year period, comprised of 106 (42%) "Tips and Falls," 84 (33%) "Component Failures," and 63 (25%) "Other" events. Sixty-eight (27%) of the incidents caused injuries requiring medical attention, including 13 hospitalizations. Direction of Tips and Falls was associated with wheelchair type (manual or powered) and with different riding surfaces. Aspects of wheelchair stability, particularly the effects of wheelchair configuration and of different riding surfaces, are important engineering issues affecting wheelchair safety. Interpretation of the results highlights wheelchair stability mechanics. Potential design improvements are discussed.