Although France is less affected by the rise in obesity than neighboring countries, the prevalence of obesity has increased, changing the distribution of this pathology in the population. We analyze this evolution by social status, education, income and gender, region of residence, using the three French national Health Surveys conducted in 1981, 1992 and 2003. The average body weight of both women and men has increased in France since 1981 and accelerated since the 1990s. This trend is obtained among all age groups. Nevertheless, this process did not affect all socioeconomic groups similarly. Geographical differences increased between north-east, where the prevalence of obesity is higher, and the Mediterranean region, where it is lower. Likewise, the gap between social and occupational categories has greatly widened: obesity has increased much faster among farmers and blue-collar workers than among managers and professionals. In contrast to women, poorer men are not more likely to be more obese than others. Our findings suggest that differences in BMI values increased substantially among social groups in France, in particular among women.