We report a 27-year-old female patient with prior history of Graves' disease and relapsing episodes of tachycardia, hyperpyrexia, muscular rigidity and coma. With the subsequent manifestation of an acute schizophreniform psychotic disorder unresponsive to neuroleptics, the primary syndrome was re-classified as febrile catatony. Hyperthyroidism was ruled out with normal serum thyroid hormone levels, as were toxic effects of thyrostatic treatment, drug-induced hypothyroidism and a malignant neuroleptic syndrome. All psychiatric symptoms subsided completely following subtotal thyroidectomy. Febrile catatatony has to be added to the spectrum of psychotic phenomena that may be caused by Graves' disease, irrespective of serum thyroid hormone levels.