Background  Recurrent, watery diarrhoea affects one‐third of patients diagnosed with irritable bowel syndrome (‘IBS‐D’). Idiopathic bile acid malabsorption (‘I‐BAM’) may be the cause.

Aim  To determine the prevalence of I‐BAM in patients suffering from IBS‐D.

Methods  A systematic search was performed of publications reporting patients presenting with IBS‐D type symptoms, who were subsequently confirmed as having I‐BAM by SeHCAT scanning.

Results  Eighteen relevant studies, 15 prospective, comprising 1223 patients were identified. Five studies (429 patients) indicated that 10% (CI: 7–13) patients had severe bile acid malabsorption (SeHCAT 7 day retention <5% of baseline value). 17 studies (1073 patients) indicated that 32% (CI: 29–35) patients had moderate bile acid malabsorption (SeHCAT <10%). 7 studies (618 patients) indicated that 26% (CI: 23–30) patients had mild (SeHCAT <15%) bile acid malabsorption. Pooled data from 15 studies showed a dose‐response relationship according to severity of malabsorption to treatment with a bile acid binder: response to colestyramine occurred in 96% of patients with <5% retention, 80% at <10% retention and 70% at <15% retention.

Conclusions  Idiopathic adult‐onset bile acid malabsorption is not rare. International guidelines for the management of irritable bowel syndrome need to be revised so that clinicians become more aware of this possibility.