BACKGROUND/AIMS: This study aimed to investigate the prevalence and characteristics of small intestinal bacterial overgrowth (SIBO) in patients undergoing abdominal surgeries, such as gastrectomy, cholecystectomy, and hysterectomy. METHODS: One hundred seventy-one patients with surgery (50 hysterectomy, 14 gastrectomy, and 107 cholecystectomy), 665 patients with functional gastrointestinal disease (FGID) and 30 healthy controls undergoing a hydrogen (Hâ‚‚)-methane (CHâ‚„) glucose breath test (GBT) were reviewed. RESULTS: GBT positivity (+) was significantly different among the surgical patients (43.9%), FGID patients (31.9%), and controls (13.3%) (p<0.01). With respect to the patients, 65 (38.0%), four (2.3%), and six (3.5%) surgical patients and 150 (22.6%), 30 (4.5%), and 32 (4.8%) FGID patients were in the GBT (Hâ‚‚)+, (CHâ‚„)+ and (mixed)+ groups, respectively (p<0.01). The gastrectomy group had a significantly increased preference in GBT+ (71.4% vs 42.0% or 41.1%, respectively) and GBT (Hâ‚‚)+ (64.3% vs 32.0% or 37.4%, respectively) compared with the hysterectomy or cholecystectomy groups (p<0.01). During GBT, the total Hâ‚‚ was significantly increased in the gastrectomy group compared with the other groups. CONCLUSIONS: SIBO producing H2 is common in abdominal surgical patients. Different features for GBT+ may be a result of the types of abdominal surgery.