High levels of child mortality in the developing countries led the United Nations to include a significant reduction of under-five mortality rates among the eight Millennium Development Goals (MDGs) to be reached before 2015. In particular, the target of MDG 4 is to reduce the under-five mortality rates in every developing country by two thirds with respect to the levels reached in 1990. This article contributes to the debate on whether the target of MDG 4 will be reached by 2015; it also offers policy recommendations. We observe 110 countries defined by United Nations as “less” or “least” developed. The time-series-macro data used in the study come mainly from the United Nations “MDGInfo” database. Additional data come from WHO, UNICEF, UNDP and World Bank databases. The availability of a large amount of comparable data at the national level makes the quantitative cross-country approach particularly suitable for describing and comparing the intensity and main features of child mortality in different regions and countries. In our article, we: 1) provide an overview of the general context of developing countries; 2) analyze (using principal component analysis and cluster analysis) aspects of child mortality to highlight its different patterns and group together the considered countries in homogeneous clusters; 3) apply and update a methodology used by international agencies to monitor the outcomes obtained by each country in the reduction of child mortality and to estimate the chance each country has to reach MDG 4 (taking into account the trends shown since 1990); and 4) utilize linear regression models to identify the main social and economic determinants of the gaps that exist for each country in 2010 between the observed under-five mortality rates levels and those required to achieve the target. Our study shows that in 50 of 110 countries, mostly in sub-Saharan Africa, the average annual rate of reduction in under-five mortality rates observed so far will not be sufficient to meet MDG 4.