Miller Fisher syndrome is a rare variant of Guillain-Barre syndrome and it is characterised by ophthalmoplegia, ataxia, and areflexia. Pupillomotor involvement occurs in approximately half of the patients with the disorder. The authors report a patient with acute areflexic mydriasis, external ophthalmoplegia, areflexia, and ataxia. Although the pupils were unreactive to light and near stimuli, administration of 0.1% pilocarpine resulted in marked miosis, suggesting cholinergic supersensitivity. Antibodies against GM1, GD1b, and GQ1b were negative. This is the first report of acute areflexic mydriasis with cholinergic supersensitivity in anti-GQ1b-negative Miller Fisher syndrome.