Intestinal capillariasis caused by , a fish-borne nematode, is an important, emerging zoonotic helminthiasis. Cases may be fatal if suitable treatment is not administered in time. We reported a hospital-based study of 85 cases in Thailand, most of which were in the northeast. All patients had a history of eating raw or insufficiently cooked fresh water fish or prawns. The clinical manifestations are characterized by chronic diarrhea, borborygmi, abdominal pain, marked weight loss, muscle weakness, fatigue, dizziness, anorexia, and edema, as well as protein and electrolyte loss. Fecal examination revealed in all patients. Although 16 of the total of 85 (18.8%) cases were initially found to be negative for using fecal examination, further examination using an immunoblotting technique found them to be positive for the IgG antibody against larval antigen. One day after administration of 400 mg of albendazole, eggs and/or larvae and/or adult were found in 16 fecal samples. After treatment with mebendazole (200 mg twice a day for 30 days) or albendazole (200 mg twice a day for 10 days), all 85 patients recovered. The potential clues for diagnosis are clinical manifestations, history of eating raw contaminated food, and positive serological test, and fecal examinations under professional. Administration of anthelminthic drugs stimulates the excretion of larvae, eggs, and/or adult worms and can be used as a supportive method for the diagnosis of intestinal capillariasis in areas where serological test is not available.