Pancytopenia can rarely complicate Grave's disease. It can be due to uncontrolled thyrotoxicosis or as a result of rare side effect of antithyroid medication. Pernicious anemia leading to Vitamin B12 deficiency is another rare associated cause. We report a case of a patient with Grave's disease and undiagnosed pernicious anemia whom was assumed to have antithyroid drug induced pancytopenia. Failure to recognize this rare association of pernicious anemia as a cause of pancytopenia had resulted in delay in treatment and neurological complication in our patient
