Since the 1970s, the incidence of thyroid cancer has been rising in France. The French Institute for Public Health Surveillance was tasked with identifying the risk factors that might explain this increase. Biological or morphological thyroid disorders have been identified as suspected risk factors for these cancers. Our study estimated the incidence of thyroid diseases and their risk factors using data collected from adults who participated in the SU.VI.MAX study and were followed for eight years. Our results show that women were more affected by thyroid diseases than men after age 45. The risk of developing hypothyroidism was higher than the risk of developing hyperthyroidism. The identified risk factors for hypothyroidism were age and alcohol consumption exceeding 15 g/day, as well as, to a lesser extent, region of residence, educational level, and parity. The incidence and factors associated with thyroid disorders are consistent with data from studies conducted in other countries. Analysis of the incidence of morphological abnormalities showed a low incidence of goiter, whereas the incidence of nodules is higher in our population than in the literature. Iodine status and urinary thiocyanate levels in men, as well as oral contraceptive use in women, were factors associated with the risk of morphological abnormalities. Few studies on morphological abnormalities have been conducted internationally, and the risk factors described in our population warrant further investigation. This study also highlights that thyroid diseases are common in the general population and provides baseline data on their prevalence in the adult population. These data are useful for identifying potential excess risks of thyroid disorders locally. (R.A.)