This was a retrospective study of patients having Gnathostoma antibody testing at the Hospital for Tropical Diseases, Bangkok during 2000-2005 to investigate predictive factors for Gnathostoma seropositivity in patients attending the Gnathostomiasis Clinic. Out of 849 patients tested, 531 (62.5%) were Gnathostoma seropositive. The median absolute eosinophil counts were 464 (0-16,796) and 326.5 (0-10,971) cells/mm3 in seropositive and seronegative patients, respectively (p<0.001). Differences in a history of cutaneous swelling, the habit of eating raw meat, eosinophilia (>500 cells/mm3), and the frequency of cutaneous swellings between seropositive and seronegative patients were all statistically significant. Patients with a history of eating raw meat and a history of cutaneous swelling were at 2.1 and 1.8 times more likely to be Gnathostoma seropositive, respectively. Logistic regression analysis showed eosinophilia was not a predictive factor for Gnathostoma seropositivity.