Background/Aim: Pterygium is a relatively frequent ocular surface disease with an unexplained etiopathogenesis. Our study was carried out with the aim to identify the presence of inflammatory cells and mediators such as T-lymphocyte subgroups (CD4 and CD8), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM- 1) and human leukocyte antigen-DR (HLA-DR) in pterygium tissue. Methods: Pterygium tissue, obtained from 24 patients, and normal conjunctival tissue, from the nasal bulbar conjunctiva obtained from 14 patients operated for ocular perforations or vitrectomy, were separated into epithelial and stromal components under the microscope and suspended with phosphate-buffered saline solution to form a suspension. Cell suspensions were treated with specific antibodies for ICAM-1, VCAM- 1, and HLA-DR and T-lymphocyte subgroups and evaluated with flow cytometry. The obtained data were compared statistically. Results: When compared to the control tissue samples, higher rates of ICAM-1- positive cells, VCAM-1-positive cells and HLA-DR-positive cells were recorded in pterygium tissue samples. CD4 and CD8 lymphocytes were also found to be at higher levels when compared to the control group. There was a statistically significant difference between the two groups. Conclusion: When compared with normal conjunctival tissue, pterygium tissue had increased levels of T-lymphocyte infiltration and inflammatory markers demonstrating the possible contribution of cellular immunity to the pathogenesis. Copyright (c) 2006 S. Karger AG, Basel.