We report the results of CaSiO3 perovskite‐melt partitioning experiments conducted at conditions relevant to the uppermost lower mantle. Partition coefficients, measured by LA‐ICPMS, show that CaSiO3 perovskite has a strong affinity for REE, Y, Th and U, making CaSiO3 the most likely host for these elements in the lower mantle. Comparison with the low‐pressure analogue CaTiO3 shows that large ions partition similarly into the Ca‐sites of the two perovskites. Thus CaTiO3 may be used as a model to investigate the factors controlling the partitioning of many trace ions into CaSiO3. Combined fractionation of MgSiO3 and CaSiO3 perovskites during an early magma ocean has been suggested as a means of enriching the lower mantle in silica. Our results show, however, that the chondritic upper mantle ratios of refractory lithophile elements would be lost after ∼17% of perovskite fractionation. A large perovskitic layer `hidden' in the lower mantle is therefore improbable.