Blastocystis hominis is a foodborne protozoan found in the human feces worldwide. One hundred and ninety-nine individuals with stool samples positive for B. hominis were identified from a pool of 14,325 patient stools collected between 2003 and 2010 from Srinagarind hospital in Thailand. The medical records of patients were reviewed for demographic and clinical data. Of the 85 patients (42.7%) who had B. hominis infection with no co-infections, 42.5% experienced gastrointestinal symptoms. Abdominal pain is the most frequently observed symptom followed by diarrhea. Strongyloides stercolaris and Opisthorchis viverrini were the predominant parasitic co-infections in blastocystosis patients. The infection rates of B. hominis were high during the rainy season. Most B. hominis-infected patients (94%) had underlying diseases; malignancy and chronic diseases were equally top ranked (35.3%) which indicated that B. hominis is an opportunistic protozoan.