The objective of this report is to summarize the available literature regarding the postnatal growth and morphological development of the brain and compare the timelines for these events between humans and experimental species. While not the primary focus of this report, in acknowledgement of the evident role of maturation of neurotransmitter systems in development, a brief description of the comparative development of the NMDA receptor is included. To illustrate the challenges faced in estimating developmental toxicity potential in humans, the importance of postnatal experience in CNS development is also briefly reviewed. This review is part of the initial phase of a project undertaken by the Developmental and Reproductive Toxicology Technical Committee of the ILSI Health and Environmental Sciences Institute (HESI) to bring together information on a selected number of organ systems and compare their postnatal development across several species (Hurtt and Sandler: Birth Defects Res Part B 68:307-308, 2003).