We previously identified an inactivating disruption of the X-linked KIAA2022 gene by a chromosomal rearrangement in two male patients with severe mental retardation. In order to determine if KIAA2022 has a role during the development of the central nervous system, we have cloned its murine ortholog, Kiaa2022, determined its genomic structure and studied its expression during mouse development. We show that Kiaa2022 is preferentially expressed in the central nervous system and that the transcript is highly expressed in postmitotic neurons. The expression of Kiaa2022 is first detectable at E10.5 to reach a maximum at P3 where it is notably expressed in the hippocampus, the entorhinal cortex and strongly in the ventral premammillary nucleus. After P3, the expression of Kiaa2022 decreases and maintains very low levels thereafter. Our results show that Kiaa2022 is expressed in the developing brain and that it may play a role in postmitotic, maturing neurons.