AbstractWe describe two patients who have hypochondroplasia with medial temporal lobe dysgenesis. This association has only been reported once before. Both patients had an FGFR3 mutation: 1620C → A, resulting in Asn540Lys. FGFR3 is expressed in the brain during development and plays a role in hippocampal formation. We suggest FGFR3 mutations might cause cerebral malformations in hypochondroplasia as well as in thanatophoric dysplasia. Further neuroimaging studies of patients with hypochondroplasia and epilepsy or developmental delay may clarify the proportion of patients with hypochondroplasia who have this pattern of central nervous system abnormalities. © 2005 Wiley‐Liss, Inc.