As mankind continues to explore beyond the confines of our planet, we must begin to consider the possibilities of serious traumas occurring in these environments. To date, there have been no major medical emergencies during a space mission, but we cannot continue to rely on luck alone, and as the space program continues to expand, these occurrences will be inevitable. In planning for emergency contingencies, one must consider the unique physiologic changes that occur in spaceflight, the microgravity or zero-gravity environment, and the constraints that occur due to the confined space and limited equipment and training and experience of personnel.