Agenesia of corpus callosum belongs to a group of cerebral malformations whose prognosis is uncertain. In such cases, assessment of prognosis may benefit from eventual associated fetal, obstetrical or familial features. We report a patient with an isolated corpus callosum agenesia that led to the discovery of a similar malformation in her father. This observation demonstrates that some forms of isolated and familial corpus callosum agenesia could have a favorable outcome. However, the difficulty of the assessment of prognosis in isolated corpus callosum agenesia is emphasized and the question of parental RMI exploration in such a peculiar context is raised.