This study brings new insights into the global diversity of the age pattern of under-five mortality. The novelty of our results relies on the newly-compiled Under-Five Mortality Database (U5MD) providing mortality information by detailed age groups, including daily, weekly, and monthly breakdowns. The fine granularity of these data allows the identication of age patterns as well as data quality issues that could not be seen previously in low- and middle-income countries. This new understanding of the age pattern of under-five mortality is necessary for detecting specific vulnerability of children at certain ages. The results will thus help guide health policy in low- and middle-income countries.