We describe a 77-year-old woman who developed a confusional state, cognitive impairment, behavioural abnormalities and dysphasia after treatment of hypercalcaemia. Repeated EEG recording revealed rhythmic sharp-wave activity over the right parietal-occipital lobe. Magnetic resonance imaging (MRI) showed marked hyperintense signal changes bilaterally. The diagnosis of a non-convulsive status epilepticus (NCSE) was made. With antiepileptic treatment the patient improved and MRI as well as EEG changes were almost all reversible. NCSE is an important differential diagnosis of patients with neuropsychiatric symptoms and can develop after rapid lowering of serum calcium levels in hypercalcaemia.