Objective To compare the effect of long-term small dose of methimazole or radioiodine 131 on bone mineral density (BMD), cardiac function, and biochemical indexes in patients with recurrent hyperthyroidism. Methods Sixty-two patients with recurrent hyperthyroidism were randomly divided into two groups: drug treatment group and radioiodine treatment group. Twenty-eight patients took a long-term oral medication of methimazole, while 34 patients were given a radioiodine treatment. During the follow-up, the thyroid function, serum lipids and lipoproteins, echocardiography, and BMD were detected. Results The thyroid function of 28 patients in drug treatment group and 13 patients in radioiodine treatment group was normal, while the other 21 patients in radioiodine treatment group had hypothyroidism. The serum levels of lipids in drug treatment group were much lower than that in radioiodine treatment group, while no difference of BMD, white blood cell, liver function, and cardiac function was observed between the two groups. Conclusion Compared with radioiodine treatment, long-term small dose of methimazole treatment is safe for patients with recurrent hyperthyroidism. [ABSTRACT FROM AUTHOR]