McCune - Albright syndrome is a rare disorder caused by an activating mutation in the gene (GNAS1) encoding the subunit of the G protein. This syndrome is characterized by polyostotic fibrous dysplasia, cafe-au-lait pigmentation, and multiple endocrine hyperfunction. A 29-year-old male with polyostotic fibrous dysplasia, cafe-au-lait pigmentations, and pituitary adenoma is presented in this report. The patient had accompanying bipolar affective disorder; which might have been caused by the underlying genetic abnormality. (c) 2007 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.