Carbon monoxide was the number 1 cause of poisoning deaths in the United States from 1980 through 1988, with the highest rates reported in the western states. We studied unintentional deaths from carbon monoxide poisoning in New Mexico during this period using the multiple-cause mortality files from the National Center for Health Statistics (NCHS) and data from the New Mexico Office of the Medical Investigator (OMI). We compared the nationally available NCHS data with the more detailed OMI data to determine the sensitivity of NCHS data for the surveillance of this preventable cause of death. The NCHS data were 88% sensitive in identifying deaths from unintentional carbon monoxide poisoning and had a positive predictive value of 81% when compared with OMI data. Half of the unintentional carbon monoxide-related deaths were attributable to a home heating mechanism of some sort, 46% involved motor vehicle exhaust, and at least 42% were associated with alcohol use. We conclude that available NCHS data are a sensitive source of surveillance information about unintentional deaths from carbon monoxide poisoning. Additional details about specific deaths can be obtained from medical examiner files when needed.