Headache with a neurological deficit and cerebrospinal fluid (CSF) lymphocytosis (HaNDL) is usually underrecognized and under-reported. HaNDL is a self-limiting condition, but the grave symptoms require a large-scale differential diagnosis. We report a case of a 24-year-old female who developed dysarthria for several hours and decreased use of the right arm with right-sided facial weakness. After extensive investigation of blood, CSF, and neuroimaging, we excluded central nervous system infections and autoimmune and vascular diseases. A diagnosis of HaNDL was made according to clinical symptoms and CSF analysis. The prognosis was good, and the symptoms resolved. Repeated physical examination after 48 h was unremarkable. HaNDL is probably not as rare as commonly thought; awareness of its existence can avoid unnecessary and potentially harmful investigations and therapies. The clinical challenge relies on the fact that it remains a diagnosis of exclusion.