Background. Lung cancer is the most common cause of paraneoplastic neurological syndrome (PNS), but there are few reports of its occurrence in cases of non-small cell lung cancer. Case. A 75-year-old woman visited our hospital with a chief complaint of dysphagia, but no organic or neurological abnormalities that could cause dysphagia were found. Chest computed tomography (CT) detected a lung nodule 1.5 cm in size in the right middle lobe and another 1.9 cm in size in the left lower lobe. Based on these CT findings, PNS due to lung cancer was suspected. Positron emission tomography (PET)/CT showed the uptake of fluorodeoxyglucose (FDG) with a maximum standardized uptake value of 5.0 only in the right middle lobe lesion, suggesting right middle lobe lung cancer (cT1bN0M0, stage IA2). Based on these findings, right middle lobectomy and lymph node dissection were performed. Pathologically, the patient was diagnosed with EGFR mutation (Exon21 L858R)-positive pulmonary adenocarcinoma (pT2aN2M0, stage IIIA). At that time, the other lesion in the left lower lobe was clinically judged to be intrapulmonary metastasis from lung cancer in the right lung, so the patient was administered osimertinib (80 mg/day). Dysphagia improved seven days after administration, and there has been no recurrence for 10 months. Conclusion. Molecular-targeted therapy for a tumor can improve PNS in EGFR mutation-positive lung adenocarcinoma.