The hippocampus is a brain structure renowned for its role in memory formation, learning and the representation of space. Hippocampal circuitry is comprised of a diverse set of excitatory and inhibitory neurons, including a transient population of reelin+ glutamatergic Cajal-Retzius neurons (CR). In contrast to neocortical CR-cells, which disappear soon after birth, hippocampal CR-cells persist for an extended period during postnatal development. These CR-cells are actively integrated into the hippocampal microcircuit; however, their influence on postnatal hippocampal development and function remains to be determined.In a recent study (Glærum et al., 2024), we used a combination of transgenic mouse lines and viral vectors to specifically ablate CR cells postnatally. CR cell ablation caused changes in dendritic complexity and spine density of CA1 pyramidal cells, significant alterations in synapse related genes and a complementary loss of synapse related proteins. We therefore investigated if CR cell ablation would also affect hippocampal function. In a simple spatial navigation task, the T-maze, characterized by a low reference and working memory load, we found that CR cell ablation resulted in a delayed learning curve. Then we challenged the mice with the radial arm maze, a task with high reference and working memory load. In this case, the animals failed to reach the same level of performance as control animals. Taken together, our findings indicate that CR cell ablation leads to deficits in hippocampal function relative to spatial memory demand, and thus underscores the importance of CR cells in the establishment of hippocampal circuitry