In the last two decades, significant strides have been made in the diagnosis and management of pituitary tumors. The identification, isolation, and characterization of the anterior pituitary hormones, the developments of sensitive and specific radioimmunoassays, and the significant advances in neuroradiologic, neurosurgical, and pathologic techniques have led to increasing recognition of pituitary tumors and their clinical syndromes. This article will review the current diagnostic approaches relating to prolactin, growth hormone-, thyrotropin-, and gonadotropin/alpha glycoprotein subunit-secretory, as well as nonsecretory, pituitary tumors.