Calcification of pituitary adenomas as a histopathologic finding is reported in up to 25% of all degenerated adenomas. On the other hand, ossification of these adenomas is an extremely rare finding, with only one reported case, a prolactinoma. Here, we report a case of somatotropinoma in a 42-year-old acromegalic female. The adenoma, about 2 cm in diameter, was removed by the transsphenoidal route. Pathologic examination revealed ossification areas in the adenoma and the patient showed dramatic progress with relief of acromegaly signs and normalization of serum growth hormone levels. This case seems to be a unique report of osteoid metaplasia of a somatotropinoma.