Horner's syndrome from hypothalamic infarction. We report a case of Horner's syndrome due to ipsilateral posterior hypothalamic infarction, occurring in the absence of other signs of hypothalamic dysfunction. Associated symptoms of contralateral faciobrachial weakness and dysarthria correlated with the extension of the infarct into the posterior limb of the internal capsule seen by magnetic resonance imaging. The likely vascular anatomy of this lesion is discussed. 