This article undertakes a longitudinal analysis of changes in black urban poverty in 59 large Standard Metropolitan Statistical Areas between 1970 and 1980. The model is based on a set of equations we derived and estimated in earlier work to test explanations of urban poverty proposed by Charles Murray (1984, Losing Ground: American Social Policy, 1950–1980, Basic Books, New York) and William Julius Wilson (1987, The Truly Disadvantaged: The Inner City, the Underclass, and Public Policy, University of Chicago Press, Chicago). The prior analysis, however, was estimated using only cross-sectional data. The present longitudinal analysis finds little support for Murray's arguments and strong support for Wilson's. Results show that structural characteristics of the urban labor market—namely the suburbanization of employment, the decline in manufacturing jobs, and the rise of low-wage services—act to reduce black male employment, increase the prevalence of female-headed families, and drive up black poverty rates; but changes in the generosity of welfare payments have little or no effect on these outcomes. Discrepancies between the cross-sectional and longitudinal analyses are reconciled by considering the likely effects of selective migration between metropolitan areas.