This would be a good topic for the Q&A webinar, but you can also find the answer by reading reading the guidelines for Chapter 20, found in guideline I.C.20. One thing that is interesting is that "There is no national requirement for mandatory ICD-10-CM external cause code reporting. Unless a provider is subject to a state-based external cause code reporting mandate or these codes are required by a particular payer, reporting of ICD-10-CM codes in Chapter 20, External Causes of Morbidity, is not required." However it goes on to indicate that providers are encouraged to voluntarily report external cause codes... and then gives the "rules" for doing so. As guidelines go, it is rather straightforward so give reading these guidelines a try!