All the cases of malignant melanoma in this study were histologically verified and this is also the case for about 94% of all registered cancers in the Cancer Registry, thus misclassification of the malignant melanomas is unlikely. Possible underregistration of malignant melanoma in the registry has not been evaluated. The pilots often attend medical examinations which may lead to earlier diagnosis of the melanomas among the pilots than among the general population. If this is the case a better survival rate and spurious increased incidence may be found among the pilots.