Primary aldosteronism resulting from an adrenal adenoma is rare in children. An 8 1/2-year-old girl was found to have hypertension and spontaneous hypokalemia, both detected as incidental findings. Subsequent investigations revealed inappropriately elevated levels of plasma and urinary aldosterone with suppressed plasma renin activity. Adrenal vein blood sampling and venography suggested the presence of left adrenal adenoma which was confirmed at surgical exploration and pathologic examination. All the clinical and biochemical abnormalities were corrected by the adrenalectomy. The differential diagnoses of various types of hyperaldosteronism and/or hypokalemia in such a clinical setting are discussed.