A 68-year-old woman and her 28-year-old son ate some rare fresh-water crabs (Eriocheir japonicus). The son became ill one month later with pleural effusion. After 10 months the mother's symptoms included cough, hemosputum and a nodular shadow on her chest X-ray. Eosinophilia was present and the Ouchterlony test showed strong bands toward Paragonimus westermani antigen in both patients. They were diagnosed as having Paragonimiasis westermani. The symptoms stopped after Bithionol administration and the bands of the Ouchterlony test also disappeared. The difference in the latent stage and clinical symptoms of these patients, who were infected at the same time, is interesting as it highlights the importance of observing other people who may have been infected with Paragonimus westermani.