Background: Hypertension is more prevalent in the African American population when compared with the European American population in the United States. Unprovoked hypokalemia may lead to hypertension and is associated with several forms of recognized secondary hypertension. Methods: We investigated the association of ethnicity with unprovoked hypokalemia in the second Atherosclerosis Risk in Communities (ARIC) study examination. Hypokalemia was defined as serum potassium <3.5 mmol/L. Results: A statistically significant association was detected between ethnicity and unprovoked hypokalemia (odds ratio = 5.3; 95% confidence interval = 3.6, 7.7) with unprovoked hypokalemia more prevalent in African Americans both before and after adjustment for important covariates. The unadjusted prevalence for unprovoked hypokalemia was 2.6% for African Americans and 0.5% for European Americans. Conclusions: We found that the prevalence of unprovoked hypokalemia for African Americans in the ARIC cohort was more than five times that for European Americans. These data suggest that an increased awareness of hypokalemia and its etiology may be indicated for African Americans.