Epidemiologic investigations have been instrumental in identifying numerous factors associated with the development of cancer. Tobacco and alcohol are unquestionably the major risk factors for squamous cell carcinoma of the head and neck region. Diet appears to play a role in the development of these cancers, as nutritional deficiencies have been found to increase risk. Clinical observation and epidemiologic studies have also identified ionizing radiation as an unequivocal risk factor, although of lesser importance from the public health point of view. Overall, epidemiologic evidence shows that occupational exposures play a minor, though definite, role in the development of head and neck cancer. For sinonasal cancer, however, studies corroborate that occupational exposures are the major determinants of disease.