The brain size of humans (Homo sapiens) has increased dramatically during the evolution of Homo. As a result, modern human brains are more than three times larger than the brains of chimpanzees (Pan troglodytes). Elucidating the similarities and differences between humans and non-human primates regarding the phylogenetic and ontogenetic mechanisms underlying brain structure is important for understanding the remarkable brain enlargement in humans. Furthermore, these biological insights will provide important clues to clarify the substrates of brain functions and mental developmental disorders seen in humans, such as autism disorders, learning disabilities, and attention deficit hyperactivity disorder. Over the past century, studies of comparative primate morphology on a number of preserved brain samples led to the proposal that prolongation of the high fetal developmental rate after birth and extension of the juvenile period were essential to promote the remarkable brain enlargement of humans and the emergence of human-specific cognitive and behavioral traits. However, the underlying phylogenetic and ontogenetic processes governing the brain enlargement observed in humans remain unclear, in part because the developmental trajectory of the brain has not been adequately explored in our closest living primate relatives, the chimpanzees. To address the above difficulty and obtain empirical evidence about the remarkable enlargement of the human brain, we tracked the development of the cerebral tissues in growing chimpanzees from the fetal period to the juvenile period using three-dimensional magnetic resonance imaging (MRI) and ultrasound scanning, and compared these results with previously recorded data from humans and rhesus macaques (Macaca mulatta). Our results reveal common features of the developmental trajectory of brain tissues among primates, common features between hominoids (humans and chimpanzees), as well as unique features of humans. In this talk, I will introduce five representative topics about our comparative imaging studies of brain development among humans and non-human primates. Finally, I will present our ongoing comparative primate MRI study performed by combining high-field MRI and cutting-edge computational neuroanatomy. This novel approach will enable us to comprehensively clarify the evolutionary similarities and differences in cortical and subcortical structures during evolution from non-human primates to the human lineage. This effort will increase our understanding of human brain circuitry and function and may ultimately contribute to better diagnosis and treatment of human mental disorders.