Headache and neurological deficits with cerebrospinal fluid (CSF) lymphocytosis (HaNDL) is a rare condition characterised by recurrent episodes of headache and transient neurological deficits. This case report presents a young patient initially diagnosed with hemiplegic migraine, having a normal brain CT, with focal cerebral perfusion mismatch not restricted to a single vascular territory on CT angiography. Brain MRI revealed a cytotoxic lesion of the splenium in the corpus callosum (CLOCC), a feature also reported in migraine. However, recurrent headaches with neurological deficits prompted further investigations with CSF analysis and brain MRI, confirming HaNDL and demonstrating reversibility of CLOCC. Recognising HaNDL as a differential diagnosis is essential in patients with recurrent headaches with focal neurological deficits, given the differences in therapeutic approach. The relationship between migraine and HaNDL is not fully understood, but they may share a pathophysiological link. Awareness of this is crucial for accurate diagnosis., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2024. No commercial re-use. See rights and permissions. Published by BMJ.)