The absence of reliable and detailed data on internal migration is a problem that repeatedly confronts demographers and population geographers concerned with the dynamics of spatial populations. The first part of this paper describes a procedure for interregional migration. An application based on data for the Soviet Union illustrates the principal argument. In the second part of the paper, the inferred migration flows are combined with fertility and mortality data in a projection of future population growth in the Soviet Union. Particular attention is focused on the changes in age compositions and regional shares of the urban and rural populations of the U.S.S.R. that might arise were fertility immediately to decline to replacement level. The paper concludes with a further examination of regularities in migration age profiles.