Olivary hypertrophy (OH) is not a primary lesion but, rather, develops as a lesion of the Guillain-Morraret triangle, which is composed of the contralateral dentate nucleus, the ipsilateral red nucleus and the ipsilateral inferior olivary nucleus. OH is usually accompanied by palatal myoclonus or other involuntary movements such as extremity myorhythmia. One case of unilateral OH following ipsilateral pontine tegmental hemorrhage is presented. Magnetic resonance imaging (MRI) showed high signal intensity in the inferior olivary nuclei on T2- and proton-density-weighted images. Enlargement of the inferior olivary nuclei was also noted. MRI may currently be the only procedure capable of confirming the diagnosis.