Composite indicators are often used to assess the structure of urban deprivation to promote sustainable development. However, the refined spatial scale of analysis poses problems related to data availability. In this paper, we define a spatial deprivation index in the province of Milan, using both census data and areal interpolation. Disaggregation methods are applied to obtain variables at lower spatial level, and a geographically weighted principal component analysis is applied to measure socioeconomic deprivation at local level. Components of deprivation are investigated in their spatial structure and some policy implications deriving from the application of a spatial approach are discussed.