Background: Hypokalemia is not an isolated disease but an associated finding in a number of different diseases. It is also a commonly neglected condition among patients with acute acetaminophen overdose. Objectives: This study intended to determine the prevalence of hypokalemia and its clinical correlates in acute psychiatric illness among hypokalemic and normokalemic patients after acetaminophen overdose. Methods: This is a retrospective cohort study of hospital admissions for acute acetaminophen overdose conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Demographic data and different types of psychiatric illness were compared between hypokalemic and normokalemic patients. Hypokalemia was predefined by a serum concentration <3.5 mmol/L. Statistical Package for Social Sciences (SPSS) 15 was used for data analysis. Results: Two hundred and eighty patients out of 305 admissions were studied. Hypokalemia was found in 63.6% of patients with a higher prevalence in the presence of psychiatric illness (67.7%). Hypokalemic patients were significantly associated with the presence of major depression (p ¼ .04), adjustment disorder (p < .001), anxiety (p ¼ .01), and suicidal attempts (p ¼ .04). Conclusion: Hypokalemia was common among patients with psychiatric illness and acute acetaminophen overdose.