Lack of disaggregated data for Native Hawaiians and Pacific Islanders (NHPIs) in the U.S. has resulted in severe gaps in understanding health disparities and unique health needs of NHPIs. Telephone interviews were conducted with 272 cancer patients identified by a population-based cancer registry. The self-reported NHPIs status was compared with that identified by the registry. Sensitivity, Specificity, Positive Predictive Value (PPV), and Negative Predictive Value (NPV) were calculated. Alternative NHPIs identification methods were explored. The registry had acceptable sensitivity (89%), specificity (96%) and NPV (99%), but low PPV (62%) in identifying NHPIs. Using additional information on surname and birthplace from the registry improved the identification of NHPIs, but either increased the false positive or decreased the counts of true NHPIs cases. Improved data collection methods and practices in identifying NHPIs in population-based cancer registries are needed and caution in interpreting cancer data for NHPIs is warranted.