Background: Despite its frequency, there is a paucity of data on risk factors for basal cell carcinoma. Objective: We assessed potential risk factors for basal cell carcinoma in a population from southern Europe. Methods: This multicenter case-control study involved 528 newly diagnosed cases and 512 controls. Results: In the multivariate analysis, red hair, lighter colored eyes, high nevus counts on the upper limbs, and the presence of solar lentigines and actinic keratoses were all associated with basal cell carcinoma. The risk of the tumor increased in subjects who reported burning easily and experiencing sunburn episodes before 15 years of age. An association was documented with indices of recreational sun exposure but no clear evidence of exposure-effect relationship was found. No relation was found with occupational sun exposure. Finally, basal cell carcinoma appeared to be significantly associated with a family history of skin tumors, a personal history of tumors other than those on skin, and radiotherapy. Conclusion: Genetic and environmental factors appear to be involved in the onset of basal cell carcinoma. (J Am Acad Dermatol 2000;42:446-52.)