Pterygium is a lesion of the corneoscleral limbus which tends to grow in size, often recurs after surgical excision and is associated with exposure to solar light. Additionally, a family history is frequently reported. Loss of heterozygosity (LOH), increased P53 expression and the presence of oncogenic viruses, such as human papilloma virus (HPV) and herpes simplex virus (HSV), have been detected in pterygia, supporting the possible neoplastic nature of the lesion. Co-infection by HSV and HPV as well as LOH at some loci have also been correlated with clinical features, such as postoperative recurrence and history of conjunctivitis. A possible model of pterygium formation is proposed, in which genetic predisposition, environmental factors and viral infection(s) participate in a multi-step process. Future research may lead to new ways of pterygium treatment such as anti-viral or gene therapy.