Pituitary tumors vary greatly in size. There is now a clinical classification of pituitary tumors that is based on morphology, primarily on the size of the pituitary tumor in diameter. According to this criterion, pituitary tumors can be classified as microadenoma, macroadenoma and macroadenoma. Microadenomas are pituitary adenomas less than or equal to 1 cm in diameter; macroadenomas are pituitary adenomas greater than 1 cm in diameter; and macroadenomas are pituitary adenomas greater than or equal to 4 cm in diameter. Microadenomas are generally more likely to occur in women and macroadenomas in men. The larger the diameter and size of the pituitary tumor, the more likely the patient will have symptoms of compression of the surrounding tissues, such as headache and optic nerve involvement. This classification is mainly related to the next surgical approach and provides guidance for the appropriate surgical approach to be taken.