Selective serotonin reuptake inhibitors are commonly used molecules in the treatment of psychiatric disorders. Among clinicians, fluoxetine is an antidepressant that is considered safe and preferred in major depressive disor-der. Many short-term and long-term effects of fluoxetine have been reported. Nausea, insomnia, headache, tre-mor, anxiety, dizziness, dry mouth, sweating, constipation, diarrhea are common and possible side effects during fluoxetine treatment. It is suggested that these side effects usually occur at the beginning of treatment and disap-pear spontaneously in the future. Hypothermia due to the use of fluoxetine has been demonstrated in animal ex-periments studies. In experimental studies, the effects of other pharmacological molecules on thermoregulation and the effect of fluoxetine on these molecules, increasing or decreasing body temperature are prominent. Clinical applications of fluoxetine for thermoregulation are directed to the treatment of female patients who develop post-menopausal fever flashes. No study reported hypothermia as a side effect after fluoxetine use in any psychiatric disorder. In this case, we present a patient who developed hypothermia following long-term use of fluoxetine. [Anadolu Psikiyatri Derg 2020; 21(4.000): 443-446]