Cancer incidence data collected by the Guam Cancer Registry for the period 1998 through 2002 were analyzed by cancer site, age, and ethnicity. Ethnicity and site specific age-adjusted cancer incidence rates for Guam residents were calculated utilizing Guam 2000 census data and the U.S. 2000 standard population and were compared to U.S. 2000 data. Age-adjusted total cancer incidence rates per 100,000 population for the major ethnic groups represented on Guam were generally lower than U.S. averages (the exception was the Caucasian group which was higher). Some highlights include: 1). Chamorros (the indigenous people of the Mariana Islands) living on Guam had a slightly lower total cancer incidence rate than the total U.S. population (406.8/100,000 vs. 478.6 U.S.). Chamorros had high age-adjusted incidence rates for cancers of the mouth and pharynx (24.4 vs. U.S. 10.7), nasopharynx (13.9 vs. 0.6 U.S.), liver (13.2 vs. 5.2 U.S.), and cervix (16.2 vs. 9.6 U.S.). Rates for prostate cancer ( 103.9 vs. 167.7 U.S.), female breast (115.9 vs. 130.9 U.S.), ovary (7.0 vs. 14.2 U.S.), colon-rectum-anus (44.3 vs. 56.9 U.S.), leukemia (11.0 vs. 12.6 U.S.), and non-Hodgkin lymphoma (7.0 vs. 18.9 U.S.) were all lower than U.S. rates. 2). Filipinos living on Guam had high age-adjusted incidence rates for cancers of the nasopharynx (5.1), and liver (9.6). Filipinos had low age-adjusted incidence rates for all cancers (215.7), cancers of the mouth and pharynx when NPC was excluded (4.8), lung and bronchus (35.6 vs. U.S. 70.1), pancreas (1.7 vs. U.S. 11.1), colon-rectum-anus (37.1), female breast (60.7), prostate (46.1), leukemia (4.7), and non-Hodgkin lymphoma (8.4). 3). Micronesians other than Chamorros had the highest age-adjusted incidence rates for cancers of the lung and bronchus (111.5), liver (39.4), and cervix (27.4). Micronesians had low age-adjusted incidence rates for cancers of the colon-rectum-anus (4.1), female breast (35.0), prostate (78.4), leukemia (6.3), and non-Hodgkin lymphoma (6.6). 4). Asians had low total age-adjusted cancer incidence rates (149.7) but had high nasopharyngeal cancer (5.4) and liver (10.7) cancer rates. Asians had low rates of cancers of the mouth and pharynx when nasopharyngeal cancers were excluded (1.4), lung and bronchus cancers (25.8), colon-rectum-anus (26.3), female breast (63.0), ovary (no cases recorded), prostate (31.3), leukemia (5.0) and non-Hodgkin lymphoma (4.9). 5).Caucasians residing on Guam had high age-adjusted cancer incidence rates for cancers of the colon-rectum-anus (91.4), female breast (148.6), ovary (34.7), and leukemia (17.7). Caucasians had low age-adjusted cancer incidence rates for nasopharyngeal cancer (no cases recorded), liver (4.0) and non-Hodgkin lymphoma (7.9). Suggestions are made for further research to explain the ethnic disparitiesin cancer incidence observed on Guam and to develop strategies for ameliorating these disparities.