The authors report two cases with Horner's syndrome and thalamic lesio
ns documented by CT and MRI. There is evidence of a right posterolater
al thalamic hemorrhage in one case and a left anterior thalamic infarc
tion in the other. The possible mechanisms of sympathetic pathway invo
lvement in these cases are discussed. In the first case, Homer's syndr
ome could be due to compression of the posterior hypothalamic area-whe
re the sympathetic pathway's superior center is supposed to be located
-or of the posterior longitudinal fasciculus, by edema resulting from
the hemorrhage. In the second case, there is evidence of a small infar
ction, which appears to be limited to the tuberothalamic territory. In
this case, the authors postulate a possible role of the thalamus in t
he development of a Homer's syndrome, perhaps by way of thalamic proje
ctions to the hypothalamic sympathetic center.