Preoperative evaluation of patients presenting for transsphenoidal resection of pituitary tumors is a very complex process, requiring careful assessment of the patient's symptoms and the proper preoperative laboratory tests. This chapter presents two case studies, which highlight the proper preoperative evaluation for different types of pituitary tumors. The first case study is about a 32-year-old male who was referred for evaluation of a possible neuroendocrine disorder. The second case study is about a 36-year-old female with the appearance of purple abdominal striae and multiple ecchymoses on her arms and legs. Cushing's syndrome (CS) is the clinical manifestation of cortisol excess, and Cushing's disease (CD) specifically describes cortisol excess caused by an adrenocorticotropic hormone (ACTH) -secreting pituitary adenoma. The treatment of CD involves surgical resection of the pituitary adenoma, because removal of the lesion and rapid normalization of the serum cortisol improves survival in these patients.