ICD-10 Code C09.0 – Malignant neoplasm of tonsillar fossa (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C09.0 – Malignant neoplasm of tonsillar fossa
What it is
C09.0 identifies a malignant tumor arising in the tonsillar fossa, the space where the tonsil sits. Use it when documentation specifies cancer of this exact anatomic site.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings may include a visible or palpable tonsillar fossa mass, throat pain, dysphagia, or referred ear pain.
When to use this code
Use C09.0 when the provider documents primary malignancy of the tonsillar fossa, including pathology or operative notes that name this site. It is also appropriate when the record clearly localizes the cancer there, even if the histology is not restated in the diagnosis line.
Do not use for
Do not use this code for benign tonsillar disease, inflammation, or unspecified oropharyngeal cancer. If the documentation names a different tonsillar or pharyngeal site, check documentation.
Coding tip
Code the exact anatomic site as documented; if the note only says “tonsil cancer,” verify whether the fossa or another tonsillar site is specified.