Quality control practices in centralized tumor registries in North America. A survey of quality control practices was mailed to 73 central registries in the U.S. and Canada. The response rate was 88%, with respondents representing a wide range of registry characteristics and reporting strategies. While registries expressed different priorities in data use, 80% of respondents felt quality control data were important in the identification of problems. The most common method of quality control was acceptance sampling (used by 97% of respondents), and took the form of visual review, recoding and edit checking. Computer-based edit checks were almost universally used (95%). Process control methods of any sort were used by only 22% of respondents with less than 4% of registries reporting formal quantitative criteria. Sixty-one percent of respondents reported conducting one or more designed studies (e.g. reabstracting or casefinding studies) but only 20% of those made the results public. Greater emphasis should be placed on development of quantitative process controls, experimental design of quality control studies, and formal analyses and reporting of study results. 