Regional and local cancer registries kept for more than 20 years allow us to monitor the number and frequency of cancers in France. The number of new cases of cancer, which reached 170,000 in 1980, recorded a 93-percent and an 84-percent increase in males and females, respectively, between 1980 and 2005. The demographic evolution of the French population explains by itself almost half of that increase. Half of the increase in frequency is due to breast cancer in women, and three quarters to prostate cancer in men, these trends being primarily due to the development of screening.