In hemithyroidectomy group (n = 19), 4 patients developed hypocalcemia, all the patients except one developing hypocalcemia in hemithyroidectomy group were having serum vitamin D levels <10 ng/ml with a mean value of 9 ± 5 ng/ml and fall in post-operative serum PTH from its pre-operative level was 30%. The gene discussed is PTH; the disease is Hypocalcemia.