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ICD-10-CM 2027

ICD-10 code for irradiation effects

T66

Radiation sickness, unspecified

Header — needs a more specific code

From the official ICD-10-CM alphabetic index entry “Irradiation effects, adverse”. Page updated September 29, 2026.

About coding irradiation effects

The ICD-10-CM code for irradiation effects is T66 (Radiation sickness, unspecified).

To report this condition, pick the subcode that matches the documentation: T66.XXXA (initial encounter), T66.XXXD (subsequent encounter) and T66.XXXS (sequela).

Don't report T66 together with the conditions in its Excludes1 note: burns (T20-T31), leukemia (C91-C95), radiation gastroenteritis and colitis (K52.0), radiation pneumonitis (J70.0) and 2 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Don't confuse with (Excludes1 for T66)

  • specified adverse effects of radiation, such as:
  • burns (T20-T31)
  • leukemia (C91-C95)
  • radiation gastroenteritis and colitis (K52.0)
  • radiation pneumonitis (J70.0)
  • radiation related disorders of the skin and subcutaneous tissue (L55-L59)
  • sunburn (L55.-)

Common questions about irradiation effects ICD-10 codes

What is the ICD-10 code for irradiation effects?

T66 — Radiation sickness, unspecified (a header code; report a more specific subcode).

Is T66 billable?

No. T66 is a header code. Report one of its more specific subcodes instead.