BACKGROUND: We describe a 40-year-old Thai woman living in Japan who was transferred to Juntendo University Hospital after lung cancer was suspected. Chest X-ray showed a nodular lesion and pleural effusion in the left lung. Laboratory data showed eosinophilia. She denied having consumed raw or undercooked food at the initial interview. Microplate enzyme-linked immunosorbent assay (ELISA) for Paragonimus westermani specific immunoglobulin (Ig) G antibody was positive at a high titer, confirming the diagnosis of P. westermani infection. She was successfully treated with oral praziquantel. All primary practitioners should be aware that paragonimiasis is an important pulmonary disease that can cause nodular lesions on chest X-ray.