OBJECTIVE: A number of factors can influence the reported outcomes of transsphenoidal surgery (TSS) for Cushing's disease - including different remission and recurrence criteria, for which there is no consensus. Therefore, a comparative analysis of the best treatment options and patient management strategies is difficult. In this review, we investigated the clinical outcomes of initial TSS in patients with Cushing's disease based on definitions of and assessments for remission and recurrence. METHODS: We systematically searched PubMed and identified 44 studies with clear definitions of remission and recurrence. When data were available, additional analyses by time of remission, tumor size, duration of follow-up, surgical experience, year of study publication and adverse events related to surgery were performed. RESULTS: Data from a total of 6400 patients who received microscopic TSS were extracted and analyzed. A variety of definitions of remission and recurrence of Cushing's disease after initial microscopic TSS was used, giving broad ranges of remission (42.0-96.6%; median, 77.9%) and recurrence (0-47.4%; median, 11.5%). Better remission and recurrence outcomes were achieved for microadenomas vs macroadenomas; however, no correlations were found with other parameters, other than improved safety with longer surgical experience. CONCLUSIONS: The variety of methodologies used in clinical evaluation of TSS for Cushing's disease strongly support the call for standardization and optimization of studies to inform clinical practice and maximize patient outcomes. Clinically significant rates of failure of initial TSS highlight the need for effective second-line treatments.