The number of new skin cancers has constantly increased in France over the past two decades. The role of sun exposure can partly explain this phenomenon and justifies the development of information and prevention campaigns to change peoples' attitude towards sun bathing. To be effective, we need to know how much information and what attitudes the population currently has with regard to the sun. Although several studies in France have targeted children, little data is available regarding adults. This trial was aimed at pinpointing the knowledge, attitude and behavior of adults regarding sun exposure. Data were collected during a randomized multicenter study on the prevention and early diagnosis of cutaneous tumors, conducted in 26 Health Centers from 1998 to 2000. Standardized questionnaires were handed to those consulting to assess their knowledge, attitudes and behavior towards sun bathing. The population was composed of 41 143 adults aged over 30, consulting one of the 26 Health Check-up units. Analysis of the data was made using SAS v 6.12 and STATA 7.0 software. Logistic regression identified the explicative factors of knowledge and behavior. All the statistical analyses were considered significant above a threshold of alpha<5%. A total of 33 021 persons filled-in the self-questionnaire. Forty-nine percent were women and 51% were men, with a mean age of 50 years. Geographically, 25% lived in the North-East, 16% in the North-West, 25 p.cent in the South-East and 34% in the South-West. Thirty percent claimed that they tanned without burning and 2% of the population studied had often suffered from sun burn, generally when they were adult. The risks related to sun burn were known, because 92% knew that the sun increased the risk of skin aging and 89% knew that it increased the risk of skin cancer. Regarding sun screens, knowledge was not so good; 42% thought that all products were the same and 53% that they allowed one to sun bathe longer. This knowledge was better in those with fair skins, in those who had a history of sun burn, in women and in those who lived in the northern areas of France. Conversely, knowledge decreased with age and was limited in those aged over 60. Regarding behavior, those with fair skin and who reddened under the sun without tanning, protected themselves more. The women declared they protected themselves more than the men, but they used less sun protective measures (clothing, hats...), other than sun screens, than men. Subjects aged over 60 protected themselves more than younger subjects. Lastly, a personal cutaneous history increased protective behavior, and those from northern France protected themselves more than those from the South. This analysis of 33 021 adults aged over 30 shows the good global knowledge of the consequences of sun bathing, but also the lack of knowledge on the interest of using external sun protection and the role of physical means of protection. Attitudes varied depending on gender, age and phototype and also depending on the area where they lived. Despite good knowledge, the most frequent behavior of adults aged over 30 is still not appropriate with differences depending on age, gender and area, which must prompt more appropriate targeting of prevention campaigns according to the populations concerned.