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The neuroleptic malignant syndrome (NMS) is a rare, but life-threatening, unpredictable and idiosyncratic reaction that has been associated with antipsychotic use. NMS is characterized by hyperthermia, muscle rigidity, altered mental status, an elevated creatine kinase (CK) level and autonomic instability. Criteria of Diagnostic and Statistical Manual of Mental Disorders fourth edition text revision (DSM IV-TR) for diagnosing NMS are severe muscle rigidity and elevated temperature associated with the use of neuroleptic medication as well as 2 or more of these; diaphoresis, dysphagia, tremor, incontinence changes in level of consciousness, mutism, tachycardia, elevated or labile blood pressure, leukocytosis and laboratory evidence of muscle injury. In Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5), symptoms are similar with DSM IV-TR but there are no criteria for NMS. The initial treatment of NMS involves discontinuing antipsychotic medications, reducing fever and maintaining hydration. In this case report, a NMS without rigidity is discussed. A 49 years old male who was admitted to the outpatient clinic for sleeplessness, loss of appetite, behavioral change, has been suffering from being doubtful and from forgetfulness for approximately two months, was hospitalized for diagnosis and treatment. Routine laboratory results on the first day of admission revealed normal findings. The patient was medicated with zuclopenthixol intramuscular (im) 50 mg, chlorpromazine 75 mg im., haloperidol 15 mg im., clonazepam 2 mg tablet (tb), olanzapine 20 mg tb in 24 hours because of agitation. The patient had fever (390C), confusion, sweating, variable systolic blood pressure (80-160 mmHg), change of consciousness in his third day of admission. There was no sign of rigidity. Biochemical parameters were found to be elevated (WBC: 12000, AST: 993, CK:38247). Possible neurological and infectious conditions were ruled out. The patient was diagnosed as having NMS. The patient was followed up in the intensive care unit. After 8 days, fever and blood tests returned to normal. In Turkey, there is not any case report about NMS without rigidity. For this reason, this case is remarkable. The other point is, if this major symptom were absent, the clinician may mistakenly diagnose an exacerbation of a primary psychiatric disorder or delirium secondary to neurological, infectious or other medical conditions, so that diagnosis may be delayed. In this case, report, we emphasized to the possibility of NMS without rigidity. DSM-5 also supports this