Aim Our unit has recently shown that sacral nerve stimulation (SNS) has a significantly positive short-term effect on selected patients with diarrhoea-predominant or mixed irritable bowel syndrome (IBS). The aim of the present prospective study was to evaluate the medium-term efficacy of SNS for IBS to establish whether SNS could have a future role in the treatment of IBS. Method Patients with IBS who had previously been implanted with a permanent neurostimulator as part of a randomized, controlled, crossover study, were assessed for medium-term follow-up. The primary end-point was change in the IBS-specific symptom score (Gastrointestinal Symptom Rating Scale-Irritable Bowel Syndrome version questionnaire) from baseline to 3-year follow-up. The secondary end-point was a change in the IBS-specific quality of life score (Irritable Bowel Syndrome-Impact Scale questionnaire) from baseline to 3-year follow-up. Results Of 26 patients, 20 were eligible for 3-year follow- up. The median IBS-specific symptom score was significantly lower at 3-year follow-up (30, range 1371) than at baseline (62, 45-80) (P = 0.0001). The effect was observed in all symptom clusters within the score. Also, the median IBS-specific quality of life score was significantly improved at 3-year follow-up (52, 26-169) compared with baseline (135, 82-180, P = 0.0002). The effect was observed in all domains of the score. As per the protocol, 75% of patients were judged therapeutic successes. Seventy per cent of patients had a more than 50% reduction in daily IBS symptoms. Conclusion At medium-term follow-up, SNS continues to be an effective treatment for highly selected patients with diarrhoea-predominant or mixed IBS.