Introduction: S100 protein and GFAP expression in pituitary adenomas tumour cells is not well known; few correlations with other prognostic or therapeutic factors have previously been reported in pituitary adenomas. We aim to elucidate their involvement in the pathogenesis of pituitary adenomas and to establish the correlation of their expression with different growth factors and growth factor receptors known to have a prognostic and/or therapeutic role. Material and methods: Sixty-one cases of pituitary adenomas were immunohistochemically assessed for the expression of GFAP and S100 protein in both tumour cells and FS cells, in close relationship with hormone profile, and correlated with vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) expression, previously studied by our team. Results: GFAP and S100 protein were expressed both in tumour cells and FS cells. Differences between morphology, distribution, and density of GFAP+ FS cells and S100+ FS cells were observed according to the hormone profile of pituitary adenomas. GFAP and S100 protein expression in tumour cells was significantly related to hormone profile of pituitary adenomas and also with VEGF and EGFR expression. Conclusions: GFAP and S100 protein expressions in tumour cells from pituitary adenomas are influenced by hormone profile. Our results support the presence of two molecular subtypes of FS cells GFAP+/VEGF+/S100 respectively and another one that is GFAP-/S100+//EGFR+ simultaneously with the classical variant GFAP+/S100+. It is possible that S100+/EGFR+ pituitary adenomas represent a group of pituitary adenomas with an aggressive behaviour and a high ability of invasion and recurrence. (Endokrynol Pol 2017; 68 (4): 380-389).