Disease of the glandular, anterior portion of the pituitary (PITUITARY GLAND, ANTERIOR) resulting in hypersecretion of ADENOHYPOPHYSEAL HORMONES such as GROWTH HORMONE; PROLACTIN; THYROTROPIN; LUTEINIZING HORMONE; FOLLICLE STIMULATING HORMONE ; and ADRENOCORTICOTROPIC HORMONE. Hyperpituitarism usually is caused by a functional ADENOMA.