Chronic illness behavior is defined by frequent visits to physicians, multiple somatic complaints, and disability disproportionate to physical findings. The prevalence of chronic illness behavior in people with irritable bowel syndrome and peptic ulcer was studied in a telephone survey of 832 people from metropolitan Cincinnati. People with irritable bowel syndrome (8% of the sample) were more likely than people with peptic ulcer (10% of the sample), and also more likely than the general population, to have multiple somatic complaints, to view their colds and flus as more serious than those of other people, and to consult a physician for minor illnesses. People with peptic ulcer were not different from the rest of the population in these regards. Chronic illness behavior appears to be learned; people who recalled being given gifts or special foods when they had a cold or flu as a child were more likely to exhibit chronic illness behavior and also more likely to have irritable bowel syndrome. These results suggest that social learning may contribute to the etiology of irritable bowel syndrome but not peptic ulcer.