A 19-year-old woman reported progressively worsening involuntary head movements since the age of 7. She had visited multiple hospitals and been labelled as having a functional disorder. Detailed evaluation identified a large supra-sellar arachnoid cyst with hydrocephalus. We made a diagnosis of bobble-head doll syndrome, which is only very rarely associated with suprasellar arachnoid cyst. Her symptoms improved rapidly following endoscopic third ventriculostomy with cyst fenestration and gradual decompression of the ventricles. Clearly, not all suppressible movements should be labelled as psychogenic.