PURPOSE: To investigate a correlation between cigarette smoking and keratoconus. METHODS: Patients with keratoconus who were treated with corneal collagen cross-linking from June 2006 to November 2007 were asked about their smoking habits. A person smoking a minimum of two cigarettes per day for more than 1 year was classified as a smoker. RESULTS: A total of 180 patients with keratoconus (mean age 28±9 years [range: 15 to 41 years]) were asked about their smoking habits. One hundred seventy-one (95%) were non-smokers and only 9 (5%) were smokers (95% confidence interval, 2.31 to 9.28). Using the chi-square test, a significant correlation was found between non-smokers and keratoconus (P<.001). CONCLUSIONS: In this group of patients with keratoconus, few were smokers. Cigarette smoke contains toxic substances. Consequently, people are advised not to smoke. However, we speculate that the by-products of cigarette smoke may lead to cross-linking of collagen, which in the cornea, may prevent the development and progression of keratoconus.