The pain can occur anywhere in the abdomen, but is most commonly in the lower abdomen and can be severe. Characteristically, it eases following the opening of the bowels. Sometimes the pain comes on after eating. When pain occurs in the upper abdomen, it can be confused with peptic ulcer or gall bladder pain and there may be an overlap with indigestion symptoms (functional dyspepsia). The site of pain can vary from person to person and even for an individual.

Diarrhoea and constipation may occur; sometimes they alternate. Morning urgency is common, where the patient feels an urgent desire to defaecate several times after getting up in the morning and following breakfast, after which the bowels may settle. There may be a feeling of incomplete emptying after a bowel movement. The motion is often described as loose and semi-formed rather than watery, but may also be described as hard and lumpy. There may be mucus present, but not blood.

A sensation of bloating is commonly reported, and the abdomen often appears visibly distended. Other symptoms are also common. The patient may complain of apparently unrelated symptoms such as headache, backache, feeling lethargic and tired. Nausea sometimes occurs, but vomiting is less common. Urinary symptoms may be associated with IBS, for example, frequency, urgency and nocturia (the need to pass urine during the night). Some women report feeling discomfort during sexual intercourse (dyspareunia).