Introduction: The aim of this study was to estimate the proportion and number of cancers attributable to lifestyle or environmental risk factors among adults in mainland France in 2015. Methods: The fraction of attributable cancer (FAC) to 13 established and modifiable risk factors (RFs) was examined among adults aged 30 years and older. It was first estimated by site and by sex for each RF, using Levin’s formula. Then, the combined AF for all RFs across all sites was estimated by sex, assuming independence among the RFs. The number of cancer cases attributable to the 13 RFs was obtained by multiplying the combined AAR by the total number of cancer cases estimated in 2015. Results: in total, 41% of cancers among adults in France in 2015 were attributable to modifiable RFs, representing approximately 142,000 cases (84,000 among men and 58,000 among women). The two main causes were smoking (20%) and alcohol (8%), for both men and women. The third cause was diet (5.7%) among men and overweight and obesity (6.8%) among women. Conclusion: A significant proportion of cancers in France (4 out of 10) could be prevented if exposure to the environmental and lifestyle factors studied were reduced to an optimal level. These results could serve as a basis for future targeted cancer prevention initiatives aimed at reducing cancer rates in France.