Two brothers are described with acanthosis nigricans and hypersomatotropism. The first had a large radiosensitive pituitary tumor with suprasellar extension and very high serum growth hormone levels that fell after radiation and transsphenoidal microsurgery. The second had no suprasellar extension and moderately high serum growth hormone levels that became normal after a cryohypophysectomy. Review of the literature on the occurrence of acromegaly or gigantism indicates that this association in families is rare. These are the first siblings who have had the diagnosis documented by measurements of serum growth hormone. We suggest that, in some patients, the presence of acanthosis nigricans may indicate the need to follow other family members for the development of pituitary tumors.