Abstract. Purpose: To evaluate the risk factors for the development of pterygium in a Middle Eastern country (Jordan) and to compare our findings with those from other countries. Methods: This study was conducted in Irbid District, in northern Jordan, a region located 31 degrees north of the equator, with a stable, subtropical climate. In this case control study, 96 adult subjects presenting with pterygium were interviewed and compared to 192 control subjects who were group-matched for age and sex. A standard questionnaire and eye examination were completed for both groups. Results: There was a strong positive association between pterygium and environmental factors. The most striking increase in the risk of pterygium occurred in subjects who worked outdoors compared to those who worked indoors, with an odds ratio of 5.47. Current and previous sunlight exposures were associated with a higher risk of developing pterygium, with odds ratios of 3.54 and 4.52, respectively. Previous use of sunglasses represented a protective element, but the protective role of recent use of sunglasses was not statistically significant. Conclusion: There is a statistically significant association between outdoor work, sunlight exposure and pterygium formation. Efforts should be made to educate outdoor workers to wear sunglasses and brimmed hats. Public education should focus on avoidance of unnecessary sunlight exposure.