EDITOR, - M C Gulliford suggests that the Royal College of Radiologists has dismissed the use of population based registries for evaluating treatment of cancer.1 Many registries have incomplete data that have been extracted by clerks from inadequate hospital case notes. In Gulliford et al's study of bladder cancer the rate of discrepancies between cancer registry data and hospital case notes was 17% for the date of first operation, 12% for the date of first radiotherapy and 16% for the radiotherapy dose.2 Only 15% of patients receiving chemotherapy were recorded as such in the registry; 28% of the case notes gave no data on …