The objective of the study was to describe the prevalences of obesity in French adults over a 9-year period. Mailed questionnaire surveys, in 1997, 2000, 2003, and 2006, sampled 20,000 representative French households by the method of quotas. Weight, height, and waist circumference were reported by all members of the selected households > or = 18-years. Obesity was defined according to the WHO criteria, BMI > 30 kg/m2. The prevalence of adult obesity increased progressively from 8.6% (95% confidence interval: 8.2-8.8) in 1997 to 13.1% (12.7-13.5) in 2006. The increase affected all ages, socioeconomic strata, and regions. Although the prevalence of obesity increased in parallel in men and women from 1997 to 2003, the rate of increase was lower in men between 2003 and 2006. These surveys showed a sharp increase in the prevalence of obesity in France in recent years contrasting with a stable prevalence in the 1980s. The results of the first Obepi surveys prompted the French government to implement a Nutrition and Health National Plan in 2001. Regular monitoring of obesity prevalence in France and neighboring countries is needed to compare future trends.