OBJECTIVES: The purpose of this study was to describe the consistency of coding of American Indians on Montana death certificates and to identify the characteristics of American Indians in Montana associated with consistent classification on death certificates. METHODS: The Billings Area Indian Health Service (IHS) patient registration file was linked with Montana Department of Health and Human Services death certificate files for 1996-1998. RESULTS: A total of 769 Montana residents who had died in 1996-1998 were matched to the IHS registration file. Of these decedents, 696 (91%) were consistently classified as American Indian on the death certificate. Seventy-two (99%) of the 73 decedents not classified as Indian were classified as white. American Indians living in counties on or near the seven Montana reservations were more likely to be consistently classified than Indians living in other counties (95% vs. 70%); those with less than 12 years of education (93% vs. 88%) were more likely to be consistently classified than those with 12 or more years of education. Decedents whose cause of death was suicide were less likely than those with other causes of death to be consistently classified (72% vs. 95%). In contrast, a higher percentage of those with an alcohol-related cause of death than of those with other causes of death were consistently classified, although this difference was not statistically significant. CONCLUSIONS: The mortality rates for Montana American Indians are underestimated overall, and are differentially under- and overestimated for selected conditions.