Magnesium is the second most abundant intracellular cation. Deficiency can cause several neurological complications, including cerebellar syndromes, with various MRI findings. These include cerebellar oedema, presumably through a similar mechanism to that in posterior reversible encephalopathy syndrome (PRES). People particularly vulnerable to deficiency include those with high alcohol consumption, excessive loss due to gastrointestinal pathology and those taking certain medications, including proton pump inhibitors. We report three patients with cerebellar syndromes associated with hypomagnesaemia. These cases support the previously reported association between hypomagnesaemia and reversible cerebellar dysfunction and illustrate the range of potential presentations. They highlight an uncommon but treatable cause of cerebellar ataxia that may present to acute neurological liaison services.