This study presents national trends in the rate of long-term illness (ALD) designations issued by health insurance funds from 1997 to 2008 for 24 cancer sites. These trends should be interpreted with caution, as they may be influenced by regulatory changes or shifts in the frequency of ALD applications among people diagnosed with a new cancer. These trends were compared with incidence rates, estimated using data from departmental cancer registries and national mortality data. Incidence estimates were based on observed data through 2004 and a projection model for the period thereafter. The study’s objectives were: 1. to verify the consistency of trends in ALD designation rates and incidence rates through 2004; 2. to identify recent breaks in trends in ALD designation rates. Over the incidence observation period (through 2004), trends in ALD designation rates and incidence rates were relatively similar, except for melanomas, bladder cancers, and laryngeal cancers. They diverged slightly, however, for a few other cancer sites. ALD enrollment rates showed clear breaks in recent trends for breast, prostate, and thyroid cancers, following several years of sustained growth. Regarding breast and prostate cancers, these trends are consistent with epidemiological knowledge; they are more unexpected for thyroid cancer, with a slowdown in the growth of the ALD designation rate after 2004 in certain age groups for both sexes. The incidence of thyroid cancer is highly sensitive to medical practices. It is possible that the effects of medical practices have plateaued or that changes in care management have begun for certain age groups. The recent and short-term trends for this cancer in France remain highly uncertain, however. (R.A.)