Objective: The objective of the following study is to compare the conjunctival graft thickness measured with anterior segment optical coherence tomography (OCT) after primary and recurrent pterygium excision. Design: Prospective, interventional and comparative study. Participants: A total of 20 eyes of 20 patients with primary pterygium (primary group) and 20 eyes of 20 patients with recurrent pterygium (recurrent group) were enrolled. Materials and Methods: All patients underwent pterygium excision with conjunctival autograft transplantation. Conjunctival graft thickness was measured at 1 week, 1 month and 3 months after surgery using the Visante-OCT (Carl-Zeiss Meditec, Dublin, CA, USA). Main outcome measure was the mean conjunctival thickness determined as the mean of three measurements at 1, 2 and 3 mm posterior to the scleral spur. Results: There were no statistically significant differences in age, sex, or laterality between the groups. Mean thickness of the graft in primary and recurrent groups, respectively, was 430 +/- 127 mu m and 461 +/- 178 mu m at 1 week after surgery (P = 0.587), 114 +/- 19 mu m and 162 +/- 48 mu m at 1 month after surgery (P = 0.001) and 109 +/- 15 mu m and 107 +/- 18 mu m at 3 months after surgery (P = 0.726). Conclusion: The findings revealed that conjunctival thickness after primary or recurrent pterygium excision was greatest at 1 week after surgery and continued to decrease for up to 3 months. Mean graft thickness differed significantly between the two groups only at 1 month after surgery.