This report presents the case of an 84-year-old woman who developed tetanus 3 days after the resection of a gangrenous small intestine caused by obturator hernia incarceration. The diagnosis of tetanus was clinically made after the appearance of generalized spastic contractions with opisthotonus. Clostridium tetani organisms residing in the gastrointestinal tract were presumed to have been endogenously inoculated into the strangulated intestine, where it produced tetanospasmin, causing tetanus. The patient successfully recovered after aggressive intensive care. There have been 16 case reports of tetanus occurring after gastrointestinal surgical procedures. Primary care physicians should thus be aware of the fact that, although extremely rare, C. tetani residing in the gastrointestinal tract can provide a possible endogenous source of tetanus infection.