The sella turcica and the surrounding area contain several different tissues varying in morphology and cytogenesis. Thus, it is not surprising that a large number of diverse lesions may arise in the sellar region. The most frequent abnormalities are the pituitary adenomas, which based on histology, immunocytochemistry, and transmission electron microscopy can be classified into several distinct entities. Pituitary adenomas originate in and consist of adenohypophyseal cells. They are usually slowly growing benign epithelial tumors, which may be associated with increased hormone secretion or may be endocrinologically nonfunctioning. Pituitary carcinomas also arise in adenohypophyseal cells. They are rare and can be diagnosed only when cerebrospinal and/or systemic metastases are documented. To illustrate the diversity, practical importance, and diagnostic difficulties, four cases were selected for presentation: lymphocytic hypophysitis, thyrotroph hyperplasia, growth hormone-producing pituitary adenoma with neuronal transformation, and composite tumor consisting of adenomatous periodic acid Schiff-positive as well as adrenocorticotropic hormone-immunoreactive adenohypophyseal cells and adrenocortical cells. The first two cases are important from a practical point of view because the proper diagnosis can easily be missed, and appropriate interpretation of the findings is essential to prognosis and treatment. The latter two cases are odd, unusual entities; their histogenesis is unresolved. Study of these and many other cases convinced us that careful and detailed morphologic investigation of lesions involving the sella turcica is of fundamental significance. Histology, immunocytochemistry, transmission electron microscopy, and, in some cases, molecular methods are essential to reach a correct diagnosis and to draw conclusions on histogenesis, growth potential, biologic behavior, prognosis, and therapeutic responsiveness.