ICD-10 Code F51.11 – Primary hypersomnia (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code F51.11 – Primary hypersomnia
What it is
Primary hypersomnia is a sleep disorder marked by excessive daytime sleepiness that is not explained by another medical, psychiatric, or sleep condition. Use this code when the chart identifies hypersomnia as the primary diagnosis.
Clinical signs
Typical findings include persistent sleepiness, prolonged sleep episodes, and difficulty staying alert during the day. Clinical features vary; refer to documentation for whether other causes have been excluded.
When to use this code
Use F51.11 when the provider documents primary hypersomnia, idiopathic hypersomnia, or a similar diagnosis and does not identify a secondary cause. It may also fit when the record states excessive sleepiness with evaluation supporting a primary sleep disorder. Check documentation if the cause is unclear.
Do not use for
Do not use this code for sleepiness due to narcolepsy, sleep apnea, medication effects, depression, or another known condition. If the chart points to a secondary cause, code that condition instead.
Coding tip
Confirm the provider’s wording and whether hypersomnia is primary, because unspecified daytime sleepiness alone may not support F51.11.