T66Header code — not billable

Radiation sickness, unspecified

Chapter
19. Injury, poisoning and certain other consequences of external causes
Category
T66
Effective date
October 1, 2026

Related codes in category T66

T66.XXXARadiation sickness, unspecified, initial encounterYesT66.XXXDRadiation sickness, unspecified, subsequent encounterYesT66.XXXSRadiation sickness, unspecified, sequelaYes

Frequently asked questions

What is ICD-10 code T66?

T66 is an ICD-10-CM diagnosis code for Radiation sickness, unspecified.

Is T66 a billable code?

No. T66 is a category/header code, not billable on its own — use one of its more specific child codes instead.

What ICD-10-CM chapter is T66 in?

T66 falls under Chapter 19: Injury, poisoning and certain other consequences of external causes.

When did T66 become effective?

T66 has been effective since October 1, 2026, per the CMS/CDC ICD-10-CM annual release.

What other codes are related to T66?

T66 belongs to category T66, which includes 3 other codes — see the related codes list on this page.

ICD-10-CM data maintained by CDC/CMS (public domain). Always verify codes with authoritative sources before making coding or billing decisions.