OBJECTIVE Miller Fisher syndrome is a localized variant of Guillain-Barré syndrome, characterized by ophthalmoplegia, areflexia and ataxia. Bickerstaff's brainstem encephalitis is a related syndrome in which upper motor neurone features accompany the classic triad. Anti-GQ1b antibodies are uniquely found in both conditions and are believed to be pathogenic. RESULTS Infectious illnesses usually precede Miller Fisher syndrome. The clearest associations have been described with Haemophilus influenzae and Campylobacter jejuni infection. Raised cerebrospinal fluid protein is seen in 60% of patients, but clinical features and anti-GQ1b antibody testing are diagnostically more informative. Experimental studies demonstrating complement-dependent neuromuscular block may be relevant to the clinical pathophysiology of Miller Fisher syndrome. Recent neurophysiological studies suggest abnormal neuromuscular transmission occurs in some cases of Miller Fisher syndrome and Guillain-Barré syndrome. Recent mouse models have demonstrated that presynaptic neuronal membranes and perisynaptic Schwann cells are targets for anti-GQ1b antibody attack. The elimination of antiganglioside antibodies from the circulation through specific immunoadsorption therapy has the potential to ameliorate the course of Miller Fisher syndrome. This condition is typically a benign, self-limiting illness. Both plasmapheresis and intravenous immunoglobulin may be employed as treatment, especially in cases of Bickerstaff's brainstem encephalitis or those with overlapping Guillain-Barré syndrome. CONCLUSIONS Anti-GQ1b antibody testing has allowed clinicians to develop a greater understanding of the spectrum of Miller Fisher syndromes and to refine clinical diagnoses in patients with unusual presentations. Experimental studies strongly suggest anti-GQ1b antibodies are pathogenic, which in principle should direct treatments towards antibody neutralization or elimination.