ICD-10-CM 2027
ICD-10 code for Nightmares
From the official ICD-10-CM alphabetic index entry “Nightmares (REM sleep type)”. Page updated September 29, 2026.
About coding Nightmares
The ICD-10-CM code for Nightmares is F51.5 (Nightmare disorder).
Within F51 (sleep disorders not due to a substance or known physiological condition), F51.5 is specifically for Nightmare disorder. Related codes cover insomnia not due to a substance or known physiological condition (F51.0), hypersomnia not due to a substance or known physiological condition (F51.1), Sleepwalking [somnambulism] (F51.3), sleep terrors [night terrors] (F51.4), other sleep disorders not due to a substance or known physiological condition (F51.8) and sleep disorder not due to a substance or known physiological condition, unspecified (F51.9).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 887 (Other Mental Disorder Diagnoses, relative weight 1.1139), in MDC 19 (Mental Diseases and Disorders), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
Common questions about Nightmares ICD-10 codes
What is the ICD-10 code for Nightmares?
- F51.5 — Nightmare disorder.
Is F51.5 billable?
- Yes. F51.5 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can F51.5 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict F51.5 as a principal diagnosis.
Is F51.5 a CC or MCC?
- No. F51.5 is neither a CC nor an MCC under MS-DRG v44.0.