Cushing's disease (CD) is caused by a pituitary adenoma secreting corticotrophin (ACTH) that leads to cortisol excess. Despite a characteristic clinical picture, it is often difficult to make a proper diagnosis, as it requires complex and long-lasting diagnostic procedures. Selective transsphenoidal surgery (TSS) remains the treatment of choice for CD. Untreated or improperly treated Cushing's disease leads to the development of serious complications, which lower patients' quality of life. Mortality in this group is high, reaching 50% within a 5-year follow-up period. In this study, we present our own experience and discuss the importance of preoperative hormone measurements, magnetic resonance imaging (MRI) of the pituitary, results of histopathological examination (immunohistochemical and ultrastructural in electron microscopy) and postoperative early and late hormonal assessment in the aspect of TSS efficacy. The performed analysis is based on the current criteria for remission of Cushing's disease. Our study emphasises the need for long-term postoperative endocrinological follow-up, which facilitates early detection of recurrent hypercortisolemia.