The de Morsier syndrome, or septo-optic dysplasia, is a developmental anomaly 
characterized by involvement of the optic system, hypothalamic-pituitary axis 
and septum pellucidum. Only a few anatomical observations are recorded. We 
report three new cases and review the pertinent literature. The 
neuropathological lesions varied as did the clinical features. The hypothalamic 
nuclei were most commonly involved, followed by the optic system and the septum 
pellucidum. Other lesions were found in the cerebral cortex, corpus callosum, 
olfactory system and cerebellum. The hypopituitarism appeared to have been 
secondary to hypothalamic damage rather than to intrinsic pituitary defect. A 
virtually normal histology and the usual endocrine cell populations were 
demonstrated by immunocytochemistry in the adenohypophysis. Damage to the 
neurophysin-containing cells of the hypothalamus explains the various degrees of 
clinically observed diabetes insipidus.