BACKGROUND: The long-term safety of administration of ramosetron in female patients with irritable bowel syndrome with diarrhea (IBS-D) is unknown. The aim of this study was to assess the long-term safety, tolerability, and outcomes with the use of ramosetron in female patients with IBS-D. METHODS: This was a phase III, open-label, uncontrolled, long-term safety trial of the treatment of female Japanese patients with IBS-D, diagnosed according to the Rome III criteria. A total of 151 patients were given 2.5 μg of ramosetron for 4 weeks, and responders continued the same dose for another 48 weeks. Non-responders at 4 weeks were given 5 μg of ramosetron for 48 weeks. At the end of week 52, 106 patients receiving 2.5 μg and 17 patients receiving 5 μg had completed the study. Safety and efficacy including symptoms and quality of life (QOL) were evaluated. RESULTS: Concerning safety, no serious adverse event related to ramosetron, specifically ischemic colitis, was observed in patients with either dose of ramosetron. However, constipation occurred in 19.7 % of patients given 2.5 μg and 10.5 % of patients given 5 μg of ramosetron. Ramosetron-treated patients showed high rates of global improvement. Stool consistency, abdominal pain and discomfort, and IBS-QOL were also improved at the last evaluation point. CONCLUSIONS: The results provide evidence of the long-term safety and efficacy of treatment with 2.5 and 5 μg of ramosetron in female patients with IBS-D. Clinicians should be aware that one-fifth of women with IBS-D receiving ramosetron may suffer from constipation during treatment (ClinicalTrials.gov ID: NCT01736423).