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Primary polydipsia (PP) is an etiologically unclear condition that characterized by increased thirst and excessive fluid intake with greater than 3L per day and which usually is coincided in patients with psychiatric disorders. The most commonly reported psychiatric disorder is schizophrenia; however, bipolar disorder is also infrequently described in concurrence. It is remarkable to note that PP could be life-threatening owing to hyponatremia which may lead seizures, cerebral edema, cardiac arrest and coma; thereby, diagnosing and treating PP are crucial. We report a case with a diagnosis of bipolar disorder, currently on remission with the treatment of lithium, presented with 5-month-history of increased water intake. A thorough clinical and diagnostic assessment revealed that patient had not any medical condition which could lead to polydipsia. It is argued that dysregulation of hypothalamic-pituitary-adrenal (HPA) axis could be the underlying reason of affective disorders and the mechanism which may lead to PP. Despite the cause of polydipsia remains unclear, we aimed to provide evidence for the associative role of HPA axis dysfunction in PP comorbid bipolar disorder. [Anadolu Psikiyatri Derg 2017; 18(0.100): 8-10]