The persistence of poverty and income inequality in less developed countries (LDCs) is a source of serious concern to development economists. To understand the structure of inequality, several researchers using a variety of methodologies have measured the importance of various contributory factors to overall income variability. The available literature—which now includes studies of Brazil, Mexico, Iran, the Philippines, Taiwan, Thailand, Pakistan, and Colombia—has been reviewed elsewhere (Fields, forthcoming). This paper presents additional evidence for urban Colombia, in the process raising some important methodological issues which bear on the design of future research studies. The data set used in this paper is described in Section I. The decomposition of Colombian inequality by functional income source is presented in Section II for micro data. Section III examines the robustness of source decomposition procedures to data aggregation. Section IV presents inequality decompositions by city, and Section V by other income-determining characteristics. Conclusions appear in Section VI.