Foulon S, et al. - Researchers used French national health insurance data to estimate the prevalence of Chronic Myeloid Leukemia (CML) in France for the year 2014. An algorithm was developed, and using a random sample of 100 potential CML patients, this algorithm was validated. Under age 20, less than 1.6 per 100 000 [1.2-2.0] was the observed crude CML prevalence, which increased to a maximum of 48.2 [45.4-51.2) at ages 75-79. Across French departments, it varied from 10.2 to 23.8 per 100 000. A high internal and external validity was displayed by the algorithm. In this study, an algorithm to recognize CML patients in administrative healthcare databases was developed and validated, which could be used for prevalence estimation as well as for future economic assessments or pharmaco-epidemiological investigations in this population.