Communist China's great effort to promote birth control in the last decade reflects its leaders' concern over population growth. Not even the Communists themselves know what the current population size is. So there is much uncertainty about even the base population from which projections are made. However, the future population depends as much on the current size as on the future growth rate. If an abrupt spurt in population did take place in the 1950s, its initial effects on the age composition might produce in the 1980s a large group in the marriageable age. The age composition and the fertility rate of the new families would be beyond the control of the Party. In this event, the race between production and reproduction would be much greater than the Communists had anticipated. Whether economic growth will be hampered depends on the rate of technological advance, particularly in agriculture. 30 pp. Ref.