A large proportion of irritable bowel syndrome (IBS) patients also complain of other functional disorders, such as headache, noncardiac chest pain, low back pain, and dysuria. Some of these features, particularly headache, may have a negative influence on the outcome of IBS. In a large proportion of female IBS patients, sexual intercourse triggers the symptoms, and frequently IBS symptoms exacerbate during menses. These gynecological-type symptoms often mislead the patients to the gynecological clinic, which may imply unnecessary investigations and inappropriate treatments. The diagnostic criteria of the fibromyalgia syndrome include IBS, and hence, the apparent relationship of both syndromes is difficult to analyze. On the other hand, no convincing evidence has been produced to date to sustain an association between IBS and the chronic fatigue syndrome.