Compartment syndrome is a surgical emergency requiring urgent release of the muscular compartments to prevent ischaemia and tissue death. Unusual presentation patterns or aetiological factors may be confusing, delaying the diagnosis and prompt management. We report a rare case of bilateral anterior compartment syndrome, secondary to psychogenic polydipsia. Compartment pressures were measured using a manometer. The patient was expedited to theatre for exploration. A literature review was performed to search for similar cases. In our case, a 42-year-old male presented confused and agitated with bilateral lower limb pain unresponsive to opiates. He had a past medical history of schizophrenia with psychogenic polydipsia, consuming 10 L of cola soft drink per day prior to presentation. Blood tests showed sodium of 112 mmol/L and a peak creatinine kinase of 13,417 U/L. On examination, he had tense and swollen bilateral anterior legs; posterior calves were soft. Left and right anterior compartment pressures were measured at 60 mmHg and 90 mmHg respectively (normal limit < 30 mmHg). At operation, bilateral fasciotomies of the anterior compartments were performed and bulging muscles were found. Reported cases similar to this resulted in permanent disability due to delays in recognising the diagnosis. Follow-up of this patient showed return of normal sensation and movement of the muscles of the anterior compartment. Hyponatraemia as a result of psychogenic polydipsia is well recognised, but isolated anterior compartment syndrome is a rare complication of hyponatraemia. This case report highlights the need to consider non-traumatic causes of compartment syndrome.Level of evidence: Level V, Diagnostic study