The small size of the study is an obvious handicap leaving us with wide 95% CIs. The strength of the study is the use of the comprehensive population registers in Iceland, the National Registry, and the Icelandic Cancer Registry. The universal use of the identification numbers made it possible to ascertain vital status for all cohort members and could secure complete identification of cancer cases in the nationwide Cancer Registry. A high proportion of the cancer cases reported to the Cancer Registry were histologically verified as already mentioned.19 The use of incidence data provided an opportunity to study cancer—such as malignant melanoma—with a good survival, an advantage compared with mortality as an end point.