Let’s face it: the ICD-10 code set isn’t exactly the most enticing reading material. So naturally, mainstream media coverage of ICD-10 has focused on some of the more, shall we say, entertaining features of the coding manual: namely, the external cause codes found in chapter 20. But while these supplementary codes certainly offer a dose of comic relief—and an endless supply of hilarious blog fodder (if we do say so ourselves)—they’ve also elicited more than a few questions. So, without further ado, here’s the rundown on what’s really going on with external cause codes.

1. They are not mandatory—at least, not in most cases.

Per the ICD-10-CM Official Guidelines for Coding and 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, even though there’s no national requirement forcing providers to report external cause codes, the coding guidelines strongly encourage medical professionals to do so anyway because the codes “provide valuable data for injury research and evaluation of injury prevention strategies.” And as this article points out, such data could provide the necessary impetus for preventative action. For example, if data showed a high incidence of injury due to motorcycle accidents in a particular region, local leaders could develop a more aggressive approach to motorcycle safety education.

2. They don’t apply to all categories of diagnosis codes.

That is, you shouldn’t submit external cause codes for every single diagnosis, because in some cases, it doesn’t make sense to attribute a condition to a specific cause. Furthermore, there are some instances in which the cause of an injury is built into the primary diagnosis code (e.g., T360X1, Poisoning by penicillins, accidental).

If it’s possible to submit external cause codes for a particular category or section of codes, you will see instructions to do so within the tabular list. Also, bear in mind that you can never submit an external cause code by itself; it always must have a corresponding principal diagnosis code.

3. There are four different types of external cause codes.

Each code answers one of the following questions:

  • How did the injury or condition happen?
  • Where did it happen?
  • What was the patient doing when it happened?
  • Was it intentional or unintentional?

You can assign as many external cause codes as necessary to explain the patient’s condition to the fullest extent possible. For example, let’s say your primary diagnosis code is S86.011A, Strain of right Achilles tendon, initial encounter. After examining the patient, you determine that the patient experienced the injury as a result of running on a treadmill at a gym. You also establish that the injury was not work-related (i.e., the patient was engaging in the activity recreationally and was not receiving compensation for it). To code for these circumstances, you would submit the following external cause codes: Y93.A1 (Activity, treadmill); Y92.39 (Gymnasium as the place of occurrence of the external cause); and Y99.8 (Other external cause status, Recreation or sport not for income or while a student).

4. You only need to report external cause codes for the initial encounter (most of the time).

Typically, you would only report place of occurrence, activity, and external cause status codes during your initial evaluation of the patient. However, there are a handful of codes—particularly ones that describe how an injury happened—that you can report more than once. These codes are usually ones that require a seventh character designating the encounter type (e.g., A, D, or S). For more on seventh characters, refer to this blog post.

5. If you submit multiple external cause codes for a single diagnosis code, you should order them according to significance.

In other words, the first cause code you list should be the one that describes the cause or intent most closely related to the principal diagnosis. Furthermore, per the official coding guidelines, external cause codes for the following events take precedence over all other external cause codes, in the following order of importance (i.e., the third-listed item trumps all items except the first and second-listed items):

  1. Child and adult abuse
  2. Terrorism events
  3. Cataclysmic events
  4. Transport accidents

Have more ICD-10 questions? We’ve got answers. Download the One ICD-10 FAQ to Rule Them All today.


While you’ll probably never have the opportunity to use any of the especially amusing external cause codes—I’m guessing there aren’t too many patients who attribute their low back pain to being struck by an orca—it’s still good to have a general idea of what these codes are all about as well as their purpose. For more nitty-gritty details on external cause codes, please refer to section 20 of the official coding guidelines. Have questions? Leave ’em in the comments section below.