Abstract: Methimazole is the first-line treatment drug of hyperthyroidism. Agranulemia is a rare but serious side effect of methimazole and has poor predictability. Through the clinical data analysis for severe agranulemia caused by methimazole to investigate the clinical characteristics, mechanism and prevention measures of the disease. During ATD medication, particularly early treatment, it should be highly alert to the occurrence of agranulemia.

Key words: hyperthyroidism, methimazole, agranulemia