Since the suborbital flight of Allan Shepard in 1961, American astronauts have logged 938 man-days in space. The Russian program has added another 1,136 man-days, including the longest mission. Psychological adjustment to the conditions of space has been generally excellent, with no major problems reported during missions. Experience thus far would suggest that psychological factors will not be a major concern on future flights. Our thesis, however, is that generalization from early spaceflights can be misleading and dangerous and that more problems in psychological adjustment can be anticipated in the future. Russian space scientists have apparently drawn a similar inference from their program. Alexei Yeliseyev, the Russian space flight director, has asserted that the only barriers to longduration spaceflights are psychological (1).