Background/aim: Increasing evidence is available about the role of prolactin in the development of various cancers. The purpose of this study is to evaluate the frequency of thyroid cancer in patients with prolactinoma followed at a single site. Materials and methods: The medical records of 182 patients diagnosed with prolactinoma were reviewed retrospectively. Serum prolactin, antithyroglobulin, antithyroid peroxidase antibody, thyroid-stimulating hormone, free T4, and free T3 values and pituitary gland magnetic resonance imaging and thyroid ultrasound reports were evaluated. Results: Forty-five (39.5%) patients were found to have a thyroid nodule (13 solitary, 32 multiple). Ten patients were administered a thyroidectomy, and differentiated thyroid cancer (DTC) was detected in 6 of these patients (6/114, 5.3%). One patient had lung metastasis. The control group consisted of 113 individuals (101 females, 12 males with a mean age of 32.1 ± 9.1). In the ultrasound reports, 28 of these individuals (24.8%) had a thyroid nodule (5 solitary, 23 multiple), and one individual (1/113, 0.8%) had DTC. Conclusion: When compared to the control group, thyroid volume and thyroid nodularity were significantly higher in patients with prolactinoma (P < 0.001, P = 0.018, respectively); however, no statistically significant difference existed for the incidence of thyroid cancer (P = 0.196).