A prospective cohort study of 3,893 shipyard workers, mainly exposed to chrysotile, indicated no increased risk of lung cancer 7-15 yrs after exposure to asbestos had ceased. The shipyard workers, however, had an increased risk of pleural mesotheliomas with 11 observed cases versus 1.5 expected. An explanation for these observations may be that asbestos may have different carcinogenic mechanisms in causing lung cancer and mesothelioma. A non-increased risk of lung cancer some years after exposure to asbestos has stopped is in accordance with asbestos acting as a promotor. The high risk of mesothelioma, on the other hand, may indicate that asbestos acts as a complete carcinogen in developing this disease.