McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia, cafe au lait pigmentation of the skin, and multiple endocrinopathies. The authors report a history of a 30-years-old man who had a pathologic humerus fracture at the age of 14 years. The diagnosis of polyostotic fibrous dysplasia was established by radiologic examinations and bone biopsy. Fourteen years thereafter, active acromegaly due to a pituitary microadenoma was diagnosed using hormone measurements and pituitary magnetic resonance imaging. Pituitary surgery was refused because of an extensive skull involvement caused by the fibrous dysplasia. After an unsuccessful therapy with bromocriptine lasting three months, long-acting octreotide (Sandostatin LAR, Novartis) treatment was started. After a 12-months course of treatment, serum growth hormone levels markedly decreased, clinical symptoms improved, but serum insulin-like growth factor I levels remained unchanged. These observations that serum insulin-like growth factor I levels failed to reflect the decrease of serum growth hormone concentrations after long-acting octreotide treatment suggest that the increased production of insulin-like growth factor I in patients with acromegaly due to McCune-Albright syndrome may involve mechanism(s) other than increased growth hormone levels.