Thyrotoxicosis-induced pancytopenia is a rare manifestation. The practical challenge is to differentiate thyrotoxicosis-induced pancytopenia from the side effects of anti-thyroid treatment following the commencement of treatment. Although some of the possible underlying pathogeneses have been reported, the complete mechanisms remain unclear concerning pancytopenia in uncontrolled thyrotoxicosis. Thyrotoxicosis-induced pancytopenia is completely reversible with the administration of anti-thyroid drugs at an appropriate time and regular follow-up to prevent further recurrence.