Transsphenoidal approach has been increasingly used in the resection of pituitary adenomas for its minimal invasiveness. However, in about 10% of these cases, the tumor cannot be totally removed due to the fibrosis. In this work, the object is to study the relationship between expression of transforming growth factor beta1 (TGFbeta1) and fibrosis of pituitary adenoma. 38 pituitary adenoma specimens were divided into fibrous group (6 cases) and non-fibrous group (32 cases). TGFbeta1 expression was detected by reverse transcript polymerase chain reaction (RT-PCR) and immunohistochemistry. Collagen content was detected by Sirius red stain. In fibrous group and non-fibrous group, respectively, (1) collagen content was 20.95% +/- 8.42% and 7.98% +/- 5.18%, with significant difference (p < 0.01); (2) TGFbeta1 mRNA was 0.79 +/- 0.15 and 0.42 +/- 0.20; TGFbeta1 protein was 0.64 +/- 0.20 and 0.32 +/- 0.40, both with significant difference (p < 0.01). Collagen deposition is a significant pathological feature in fibrous pituitary adenomas. TGFbeta1 may play an important role in the fibrosis of adenoma.