The perirhinal and parahippocampal cortices are key components of the medial temporal lobe memory system and essential for the processing of spatial and declarative memory. In humans, major changes in declarative memory capacities occur within the first seven years of life, but until recently, the neurobiological substrates underlying these changes remained hypothetical. Previous studies have shown that distinct regions, layers and cells of the hippocampus and entorhinal cortex exhibit different profiles of structural and molecular development during early postnatal life. Accordingly, the differential maturation of distinct hippocampal circuits is thought to underlie the differential emergence of specific "hippocampus-dependent" memory processes. To better understand the maturation of the primate medial temporal lobe memory system, we implemented design-based stereological techniques to characterize the structural development of the different layers and subdivisions of the perirhinal and parahippocampal cortices in macaque monkeys at different postnatal ages. We found different developmental changes in neuronal soma size, neuron number and volume of the distinct layers and subdivisions, which overall suggest an earlier maturation of the parahippocampal cortex compared to the perirhinal cortex, and an earlier maturation of the superficial layers relatively to the deep layers. These findings are consistent with studies showing the differential maturation of the rostral and caudal entorhinal cortex, which are interconnected with the perirhinal and parahippocampal cortices, respectively. This study provides fundamental information on the normal development of the primate medial temporal lobe memory system and define critical periods of maturation that might be sensitive to perturbation and contribute to developmental disorders.