OBJECTIVE: Our aim was to investigate the thyroid function tests and thyroid volume differences among males with isolated hypogonadotropic hypogonadism (IHH) who take androgen replacement treatment (ART). MATERIALS AND METHODS: Forty-four male with IHH with a mean age 33.2 (18-54), diagnosed in Endocrinology and Metabolism Department between September 2013 and September 2014 and 40 healthy male control with a mean age 27.77 (18-55) were involved to study. Patient group was divided to testosterone-treated patients (n = 19) and human chorionic gonadotropine (hCG)-treated patients (n = 25). Patient group was compared in terms of total testosterone, thyroid function tests [thyroid stimulating hormone (TSH), free thyroxine (fT4)] and thyroid volume, before and 6 months after treatment. Patient group was compared with control group as well. RESULTS: When we compared the patient group with the control group, there was no significant difference for age, Body mass index, TSH, fT4 and thyroid volume between two groups before treatment. There was no difference in terms of TSH, but fT4, testosterone levels and thyroid volume were significantly higher after treatment, when the patient group was compared before and after treatment (p < 0.05). When we compared testosterone-treated patients and hCG-treated patients; thyroid volume was higher among hCG-treated patients (p = 0.001) but there was no difference for thyroid volume before and after testosterone treatment (p > 0.05). There was no statistically significant correlation between testosterone levels with TSH, fT4 and thyroid volume (r = 0.09, p = 0.32; r = 0.14, p = 0.11; r = 0.15, p = 0.09, respectively). CONCLUSION: Our study showed that ART increases the thyroid volume especially in hCG-treated patients. Therefore, we suggest that thyroid volume changes should be followed up in hCG-treated patients.