RATIONALE: One-and-a-half syndrome (OAAH) is characterized as the combination of 
ipsilateral horizontal gaze palsy and internuclear ophthalmoplegia. OAAH 
syndrome accompanied with 7th and 8th cranial nerve palsy is called 
16-and-a-half syndrome. We aimed to report the case of 16-and-a-half syndrome 
with metastatic pons tumor.
PATIENT CONCERNS: A 57-year-old male diagnosed with nonsmall-cell lung cancer 
(NSCLC) with brain metastasis occurring 15 months ago was referred to our clinic 
with the chief complaint of horizontal diplopia and right gaze palsy.
DIAGNOSIS: According to the patient symptom, ocular examination, and 
radiographic findings, he was diagnosed as 16-and-a-half syndrome which was 
caused by brain tumor metastasis from NSCLC.
INTERVENTIONS: We referred him to hemato-oncology department and he was treated 
with radiation and supportive therapy.
OUTCOMES: Unfortunately, the patient passed away 1 month later without 
improvement of ophthalmoplegia.
LESSONS: The clinical findings of our case indicate 16-and-a-half syndrome 
caused by brain tumor metastasis from NSCLC, which to our knowledge has not been 
previously reported. The case highlights a rare cause of OAAH spectrum disease 
and the importance of a systemic work-up including associated neurologic 
symptoms and brain imaging in patients with horizontal gaze palsy.