This study compared the number of mast cells and histopathologic findings in 140 randomly selected pterygium and 30 normal conjunctival specimens. The pterygium specimens came from medical centers in two regions of Turkey with different climatic conditions (Adana with high sunlight exposure and Ankara with relatively low UV ray exposure). Slides were stained with routine H&E and toluidine blue to detect mast cells. The mean mast cell counts for 140 pterygium and control specimens were 17.9±8.39 and 9.23±6.86 and the difference was statistically significant (p<0,05). The mean counts estimated in Adana and Ankara specimens were 18.44±8.77 and 16.51±7.23 respectively without any statistically significant difference. The pterygium specimens from Adana (n=101) had demonstrated a significantly higher frequency of inflammation (six times higher) than those from Ankara (n=39). This finding is related to increase of mast cell degranulation via ultraviolet rays. The results suggest that mast cells are actively involved in the pathogenesis of pterygium and ongoing changes in these lesions and many factors other than UV rays might directly influence or induce mast cell-related effects that are involved in the pathogenesis of pterygium.