The molecular components of the mitochondrial Ca2+ uptake machinery have been only recently identified. In the last months, in addition to the pore forming subunit and of one regulatory protein (named MCU and MICU1 respectively) other four components of this complex have been described. In addition, a MCU KO mouse model has been generated and a genetic human disease due to missense mutation of MICU1 has been discovered. In this contribution, we will first summarize the recent findings, discussing the roles of the different subunits of the mitochondrial Ca2+ uptake complex, pointing to the current contradictions in the published data, as well as possible explanations. Finally we will speculate on the recent, totally unexpected, results obtained in the MCU knock-out (KO) mice.