Neuroleptic malignant syndrome (NMS) is a movement disorder emergency requiring immediate identification and treatment. This syndrome is characterized by several clinical symptoms, such as rigidity, hyperthermia, altered mental state, and autonomic dysfunction. Neuroleptics are the most reported causative agents for NMS. An idiosyncratic reaction is one of the hypothesized mechanisms, and the patient usually develops symptoms 24-72 hours after drug administration. Here we present a rare case of delayedonset NMS that occurred after repetitive neuroleptic injections. The patient, a 51-year-old male, experienced NMS 6 months after multiple injections of long-acting haloperidol decanoate. He received dopamine agonist therapy and had to be hospitalized for almost 4 weeks owing to NMS symptom fluctuation. He was eventually discharged without any neuroleptic drugs. Clinicians should be aware that repetitive injections of a long-acting antipsychotic might induce delayed-onset NMS, and its slow and sustained release properties might contribute to a prolonged and fluctuating clinical course. © 2020 Nova Science Publishers, Inc..