All accidental carbon monoxide poisoning should be preventable. Yet despite intervention efforts including promotion of inexpensive home carbon monoxide detectors, annual inspection of home gas and oil appliances, and general awareness campaigns, in 2002 there were 18 fatalities, 36 inpatient admissions, 351 emergency department visits and 117 poison center calls attributed to acute carbon monoxide exposure. The first step to help better focus public health interventions is adequate information on occurrences. The Wisconsin Environmental Public Health Tracking program identified and evaluated potential data sources for inclusion in a surveillance system for monitoring unintentional carbon monoxide poisonings. Criteria to evaluate the utility of the existing data systems were developed and included the number of new cases identified from that source, the circumstantial detail provided, timeliness of data availability, confidence that an actual exposure occurred, and the resources required to retrieve and summarize the data. Five candidate datasets were evaluated: emergency department visits, hospital inpatient stays, death certificates, Wisconsin Poison Center records, and newspaper reports. It was found that although there was some overlap between cases reported in the different datasets, each source provided unique cases. The sources also differed in the resources required for utilizing the data and the amount of circumstantial information provided. Based on the evaluation of the different sources, it was concluded that newspaper reports should not be included, but the other 4 data sources would each contribute substantially to establishing a comprehensive surveillance system for accidental carbon monoxide poisoning.