We report a case of severe hypomagnesemia, hypokalemia and hypocalcemia in a 55-year-old lady who defaulted her treatment twice for pulmonary tuberculosis and presented with tetany to the emergency room. Hypocalcemia and hypokalemia persisted despite adequate correction and improved only after the correction of hypomagnesemia. The biochemical abnormalities were further complicated by streptomycin therapy necessitating to modify the anti-tuberculous regimen. The association of hypomagnesemia with tuberculosis is reported earlier and this association is attributed to renal magnesium wasting following aminoglycoside containing anti tuberculous regimen. However, hypomagnesemia contributing to hypocalcemia and hypokalemia, occurring as a primary abnormality in patients with tuberculosis is reported rarely. Here we report a case of active pulmonary tuberculosis who presented with such rare manifestations. This report emphasizes the need to maintain a high index of clinical suspicion of hypomagnesemia in patients with tuberculosis and in those receiving aminoglycoside as a part of their anti tuberculous therapy (ATT).