OBJECTIVE The idea that reactive oxygen species (ROS) are associated with the pathogenesis of inflammatory periodontal diseases and have a role (direct or indirect) in tissue damage has become a major area of research over the last decade. The purpose of this study is to determine, presence of 8-isoprostane in gingival crevicular fluid (GCF) in healthy, gingivitis and chronic periodontitis (CP) subjects and to find an association, if any between GCF 8-isoprostane levels and clinical periodontal parameters. METHODS 78 subjects (40 males and 38 females) were selected based on their clinical parameters into three groups: Group 1 (26 healthy), Group 2 (26 gingivitis subjects) and Group 3 (26 CP subjects). GCF 8-isoprostane levels were estimated by ELISA. RESULTS The 8-isoprostane concentration in GCF was highest in subjects with chronic periodontitis as compared to gingivitis and healthy subjects and a significant association was observed between GCF 8-isoprostane levels and all periodontal parameters. CONCLUSIONS There was increase in 8-isoprostane levels in GCF as the disease process progressed from health to gingivitis and chronic periodontitis, suggesting a role for increased oxidative stress in CP.