Background <p>Holmes tremor (HT) is a rare, symptomatic movement disorder characterized by a low-frequency tremor present at rest, with postural and intentional components. It is typically caused by combined lesions affecting both the dopaminergic nigrostriatal and cerebello-thalamic pathways. Brainstem cavernous malformations (particularly those involving the midbrain) are an unusual but documented cause of HT. Management is challenging, often requiring surgical or neuromodulatory interventions when pharmacologic treatment fails.</p> Case presentation <p>We report the case of a 35-year-old previously healthy woman who presented with a thunderclap headache, right oculomotor nerve palsy, and left hemiparesis. One month later, she developed a disabling low-frequency, high-amplitude tremor in the left upper limb. Neurological evaluation and MRI revealed a right tegmental midbrain cavernoma involving the red nucleus. The clinical presentation was consistent with Holmes tremor and Benedikt syndrome. Pharmacological treatment with dopaminergic agents, anticholinergics, beta-blockers, and anticonvulsants over several years failed to provide relief. Due to persistent disability and rebleeding risk, the patient underwent microsurgical resection via a subtemporal approach using the lateral mesencephalic sulcus safe-entry zone. Gross-total resection was achieved. Postoperatively, she experienced transient diplopia and improved ptosis. Tremor markedly improved over subsequent months. At one-year follow-up, the patient remained functionally independent with near-complete tremor resolution.</p> Conclusion <p>Holmes tremor secondary to midbrain cavernous malformation is exceedingly rare, with few cases demonstrating significant improvement following lesion-targeted surgery. This case highlights the clinical and surgical relevance of safe-entry zones in brainstem cavernoma management and supports microsurgical resection as a viable therapeutic option in select patients with medically refractory HT.</p>