The aim of this study was to investigate the relationship between body mass index (BMI kg/m2), the inflammatory mediator tumor necrosis factor alpha (TNFalpha), and interleukin-8 (-8) in gingival crevicular fluid (GCF) from 32 obese subjects aged between 13 and 24 years. Gingival inflammation (GBI %), pathological pocket depths, and alveolar bone loss diagnosed on radiographs were recorded. The GCF was collected from six sites per subject using periopaper, and the volume was determined using Peritron 8000. The levels of TNFalpha and IL-8 were determined using ELISA kits. Within the whole group, there was no significant relationship between BMI and the variables age, GBI %, number of periodontal pockets, smoking, and the levels of TNFalpha or IL-8. In subjects with BMI > or =40, however, there was a statistically significant correlation (r= 0.74, P< 0.01) between the level of TNFalpha in GCF and BMI. The correlation coefficient between BMI and TNFalpha in subjects with BMI > or =40 differed significantly (P< 0.05) compared to that between subjects with BMI <40. The level of TNFalpha in GCF was positively correlated (P< 0.05) with BMI in subjects with no periodontal pathological pocket. No significant correlation was found between the level of IL-8 and BMI. The results indicate that BMI positively correlates with TNFalpha in GCF in the group of young subjects with BMI > or =40 as well as in the subjects with no pathological periodontal pocket (> or =4 mm) and that TNFalpha in GCF may be affected by the obese condition through a systemic effect.