Despite the fact that pituitary adenomas are among the most frequent brain tumours, TSH-secreting pituitary adenomas (thyrotropinomas) are less than 1% of all adenomas. Due to the increase in the free fractions of thyroid hormones at normal or elevated TSH levels, the majority of patients with these pituitary adenomas have a long anamnesis of thyrotoxicosis which requires a differential diagnosis with thyroid pathology (Graves’ disease, toxic adenoma, autonomously functioning thyroid nodules). The diagnosis of the thyrotropinoma is quite challenging for clinicians. This article describes the case of a combination of the thyrotropinoma with primary hypothyroidism as a result of the Hashimoto’s disease. A feature of this article is the absence of a typical clinical picture of thyrotoxicosis in combination with an evaluated level of TSH on the background of constantly increasing substitution therapy for primary hypothyroidism. The picture of space-occupying lesion according to MRI of the brain allowed to suspect hormone-active pituitary adenoma (macroadenoma). As a result of surgical treatment (endonasal transsphenoidal adenomectomy), the level of TSH and free thyroid hormone levels were normalized in the postoperative period. The diagnosis of TSH-secreting pituitary adenoma was confirmed by histological and immunohistochemical analysis of postoperative material.