This study evaluated occurrence of travel and travelers' diarrhea in patients with irritable bowel syndrome (IBS). A survey was mailed to 591 patients of a clinical practice who had IBS. Based on survey responses, patients were categorized as having IBS, post-infectious IBS (PI-IBS), unclassified functional bowel disorder (UFBD), or post-infectious UFBD (PI-UFBD). Of 201 persons who returned questionnaires meeting inclusion criteria, 57.7%, 11.4%, 24.9%, and 6.0% had IBS, UFBD, PI-IBS, and PI-UFBD, respectively. Travel during six months before illness onset was more common in patients with PI-IBS or PI-UFBD than in persons with idiopathic IBS or UFBD (P = 0.006). Survey results demonstrated that 16.1% of post-infectious bowel disorder cases and 7.5% of overall IBS cases in a general medical population developed chronic disease within six months of an international trip. Symptoms of established functional bowel disorder in each clinical category were shown to worsen after travel-related acute diarrhea.