We report a patient with tuberculosis treated with a five-drug regimen who experienced severe acid-base and electrolyte abnormalities including hypomagnesemia, hypokalemia, hypocalcemia, and a hypochloremic metabolic alkalosis. These disturbances are believed to be due to treatment with capreomycin, which produced renal magnesium wasting and possible tubular damage. Therefore, we recommend frequent determinations of serum electrolytes, magnesium, and calcium in patients treated with capreomycin.