This work sets forth a vision for space medicine as it applies to deep-space voyage. As space missions increase in duration from months to years and extend well beyond Earth's orbit, so will the attendant risks of working in these extreme and isolated environmental conditions. Hazards to astronaut health range from greater radiation exposure and loss of bone and muscle density to intensified psychological stress from living with others in a confined space. Going beyond the body of biomedical research, the report examines existing space-medicine clinical and behavioural research and health care data and the policies attendant to them. It describes why not enough is known today about the dangers of prolonged travel to enable humans to venture into deep spae in a safe and sane manner. The report makes a number of recommendations concerning NASA's structure for clinical and behavioural research, on the need for a comprehensive astronaut health care system and on an approach to communicating health and safety risks to astronauts, their families and the public.