The use of three-point occupant restraints has been shown to be a very effective means of reducing the severity of occupant injuries over all crash modes. In a small number of cases, not involving intrusion into the occupant space, severe to fatal injuries have occurred to fully-restrained occupants, and restraint system misuse has been found to be a maior causal factor. Three primary modes of seat belt misuse are identified in the present paper, these being excessive slack in the system, improper placement of the seat belt webbing, and unsuitable pre-impact posture of the occupant. The consequences of such seat belt misuse are examined through case studies of real-world collisions which have been the subjects of multi-disciplinary investigations by the authors. Such instances underscore the necessity of improving the design and performance of current restraint systems, and of providing suitable public education as to the correct manner in which seat belt systems should be utilized.