PURPOSE: It was aimed to compare the testosterone level during the treatment and the factors associated with the persistence of hypogonadism in prolactinoma. MATERIAL AND METHODS: Thirty-five patients with hypogonadism who were diagnosed with prolactinoma were recruited to this retrospective study. Age, hemoglobin, hematocrit, glucose, lipid parameters, prolactin, follicle-stimulating hormone, luteinizing hormone, total testosterone, and the adenoma size were compared at the baseline and 6th month of the treatment. The parameters were also compared between the patients with hypogonadism (n=8) and the patients without hypogonadism at the 6th month of the treatment (n=27). Correlation analysis was also performed in terms of parameters that may be associated with the testosterone levels at the 6th month of the treatment. RESULTS: The mean current age of the whole study group was 45.6±13.0 years, and the mean adenoma size was 23.9±11.4 mm. Thirty patients had macroadenoma, and five patients had microadenoma. Eight patients (23%) had low testosterone levels and hypogonadism symptoms at the 6th month of the prolactinoma treatment. The adenoma size was larger in patients with persistent hypogonadism than the patients without hypogonadism at the 6th month of the treatment, while the prolactin levels were similar between the groups, and macroadenoma was detected in all patients with persistent hypogonadism. A negative correlation was found between the testosterone levels at the 6th month of the prolactinoma treatment with the adenoma size. CONCLUSION: Adenoma size is the prominent factor than prolactin levels for predicting persistent hypogonadism in patients with male prolactinoma.