Irritable Bowel Syndrome (IBS) is characterized by an alteration of the frequency of the intestinal evacuations, which are associated with abdominal discomfort. The etiology of this health problem is not very well known yet. The psychological literature offers support to IBS comprehension by stress model, adjunctive bowel motility model and operant model. This study was an exercise in functional analysis of behavior with a woman, IBS patient, through interviews and self-monitoring (SM) of daily activities and the symptoms to verify the existence of functional relations between these two events. The participant showed a diarrhea symptom which had a consistent remission during a period of vacation, as a function of changes in the academic demands. Her symptoms seemed postponing aversive activities, indicating the operant control. This study demonstrated the possibility of using functional analysis as an instrument capable of helping in SII comprehension.