The aim of this study is to evaluate aromatase expression in prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) secreting cells. Nontumoral human pituitary specimens were obtained from autopsy samples. Aromatase co-expression was determined by double immunohistochemical staining and assessed using H scores. H scores for GH-aromatase co-expression (GH-aromatase), TSH-aromatase co-expression (TSH-aromatase), and PRL-aromatase co-expression (PRL-aromatase) were 83.1 +/- A 13.1, 95.6 +/- A 16.1, and 83.7 +/- A 14.5, respectively. TSH producing cells exhibited the highest H score for co-expression of aromatase (p < 0.001). There was no gender difference in terms of H scores for aromatase expression and double immunohistochemical staining results (p > 0.05 for all). There was a negative correlation between the H scores for aromatase and PRL-aromatase, GH-aromatase and TSH-aromatase, respectively (r = -0.592, p < 0.001; r = -0.593, p < 0.001; r = -0.650, p < 0.001, respectively). Also, H scores for aromatase co-expression of each hormone were negatively correlated with the H scores for the corresponding hormone (r = -0.503, p < 0.001 for PRL-aromatase and PRL; r = -0.470, p < 0.001 for GH-aromatase, and GH; r = -0.641, p < 0.001 for TSH-aromatase and TSH). H scores for mean aromatase, GH-aromatase, TSH-aromatase were invariant of age (p > 0.05 for all). Age was negatively correlated with PRL-aromatase H score (r = -0.373, p = 0.008). Our study demonstrated significant aromatase co-expression in PRL, GH, and TSH secreting cells of the human anterior pituitary gland. The mutual paracrinal regulation between aromatase and three adenohypophyseal hormones indicates that aromatase may have a regulatory role on the synthesis and secretion of these hormones.