The article’s main tasks include analyzing changes in the main parameters of Ukraine’s demographic sustainability before the current full-scale war (1989–2021) and assessing the quantitative, structural, and territorial demographic changes caused by it. The databases of the State Statistics Service of Ukraine and the International Organization for Migration, official reports of the Ukrainian Government, and expert data are the primary sources of demographic statistics. I used the index analysis tools to study changes in the reproductive and age-sex balances in Ukraine and its regions. Since the mid-1990s, Ukraine has been experiencing a deepening demographic reproduction crisis, manifested in a large-scale population decline and a deterioration in age and gender balance. Using the cluster analysis method, the demographic zoning of Ukraine is carried out. Russia’s full-scale invasion has catastrophically weakened Ukraine’s demographic sustainability. As a result of the war, tens of thousands of Ukrainian citizens died, and millions migrated, which deepened significant deformations in the sex and age structure of the population. The obtained results can be used to develop social and demographic policy measures. The study’s limitations are related to the lack of reliable migration data.