The opsoclonus–myoclonus syndrome is a rare and distinct neurological disorder characterised by rapid multidirectional conjugate eye movements (opsoclonus), myoclonus and ataxia, along with behavioural changes in adults and irritability in children. Sometimes it is due to a self-limiting presumed para-infectious brainstem encephalitis but it may also represent a non-metastatic manifestation of neuroblastoma in children and small cell carcinoma of the lung in adults. In this article, we will describe the clinical features, diagnosis, pathogenesis and management.