A matched case-control study was undertaken to assess the relative risk associated with known and suspected risk factors of squamous cell carcinoma of the skin among patients in the Montreal region. Three hundred eleven cases histologically diagnosed in 1977 and 1978 in 12 hospitals and meeting strict definition criteria were identified. With the exception of six cases, two controls were matched to each case for sex, age, and hospital of diagnosis. A logistic regression analysis was done. The known host risk factors (eye and hair color, complexion, descent) and nonoccupational sunlight exposure were found to be operative in the Montreal region. After adjusting for these factors, occupational sunlight exposure appeared to be a risk factor. An association was then observed between the risk of squamous cell carcinoma of the skin and tobacco smoking and the use of a sunlamp. Relative risks associated with the above-mentioned factors were estimated.