The Guam Cancer Registry (GCR) collects data on cases of cancer in Guam residents whether their initial diagnosis is made on Guam or as a result of a referral to an off-island medical facility. It also collects data on cancer of non-residents diagnosed on Guam. Although including non-Guam resident cancer cases in statistical tables will have the effect of raising local cancer rates, this probably only partially compensates for the number of Guam-resident cancer cases that are diagnosed off-island and not reported to the registry. Cases are also collected by a periodic review of death certificates filed with the Guam Office of Vital Statistics. To test this hypothesis GCR records were reviewed to determine the number of reported cancer cases for each ethnic group that claimed to be Guam residents. Since a high proportion of cancers seen among Micronesians on Guam represent cases referred from their home islands, it may also be that these cases only represent those cancers most likely to be referred to Guam rather than being representative of the cancers most commonly occurring within these ethnic groups in their home islands.