["To observe the changes of sex hormones and sexual function in male patients with Graves' disease (GD) after Radioiodine-131 (I-131) therapy.", "Thirty-four male GD patients, aged 21 -40 (32.3 +/- 6.7) years, were treated with I-131 at the dose of 111 - 407 (237.8 +/- 51.8) MBq. The levels of serum sex hormones were measured, and the patients'scores on erectile function (IIEF-5) were obtained before and 3 and 6 months after the treatment. Another 20 healthy men aged 25 - 37 (31 +/- 3.1) years were enlisted as controls.", 'The baseline levels of estrogen (E2), testosterone (T) and luteinizing hormone (LH) were (132.5 +/- 40.4) pmol/L, (21.6 +/- 4.6) nmol/L and (10.1 +/- 4.4) IU/L in the GD patients, significantly higher than (80.4 +/- 31.2) pmol/L, (14.5 +/- 4.2) nmol/L and (6.2 +/- 1.9) IU/L in the healthy controls (P < 0.05). The E2, T and LH levels showed a significant decrease in the GD patients after 3 months of treatment ([110.2 +/- 20.6] pmol/L, [17.7 +/- 5.5] nmol/L and (9.4 +/- 3.9) IU/L, P < 0.05), but exhibited no statistically significant differences from the healthy controls at 6 months ([82.6 +/- 30.1] pmol/L, [13.8 +/- 3.4 ] nmol/L and [6.6 +/- 1.5] IU/L, P > 0.05). The IIEF-5 score of the GD patients was 5 - 25 (15.5 +/- 3.5) before I-131 treatment, significantly lower than that of the controls (19 - 25, 24 +/- 0.5) (P < 0.05), and it was 8 - 25 (19.5 +/- 1.0) at 3 months and 10 - 25 (23.5 +/- 1.5) at 6 months, significantly higher in the latter than in the former (P < 0.05), and with no significant difference between the 6-month treated patients and the healthy controls (P > 0.05).'] Does [ Radioiodine-131 therapy improve sex hormones and sexual function in male patients with Graves ' disease ]?