The natural course of untreated neuroleptic malignant syndrome (NMS) does not usually exceed 3 weeks. Its duration is reduced by dantrolene and/or bromocriptine. We report a patient in whom NMS developed after an injection of haloperidol decanoate and fluctuated during 3 months. This was due perhaps because the initial treatment with oral neuroleptic was pursued, or because the doses of dantrolene were insufficient.