Aims: To assess healthcare resource use and costs among irritable bowel syndrome (IBS) with diarrhea (IBS-D) patients with and without evidence of inadequate symptom control on current prescription therapies and estimate incremental all-cause costs associated with inadequate symptom control. Methods: IBS-D patients aged >18 years with >1 medical claim for IBS (ICD-9-CM 564.1x) and either >= 2 claims for diarrhea (ICD-9-CM 787.91, 564.5x), >= 1 claim for diarrhea plus >= 1 claim for abdominal pain (ICD-9-CM 789.0x), or >= 1 claim for diarrhea plus >1 pharmacy claim for a symptom-related prescription within 1 year of an IBS diagnosis were identified from the Truven Health MarketScan database. Inadequate symptom control, resource use, and costs were assessed up to 1 year following the index date. Inadequate symptom control included any of the following: (1) switch or (2) addition of new symptom-related therapy; (3) IBS-D-related inpatient or emergency room (ER) admission; (4) IBS-Drelated medical procedure; (5) diagnosis of condition indicating treatment failure; or (6) use of a more aggressive prescription. Generalized linear models assessed incremental costs of inadequate symptom control. Results: Of 20,624 IBS-D patients (mean age = 48.5 years; 77.8% female), 66.4% had evidence of inadequate symptom control. Compared to those without inadequate symptom control, patients with evidence of inadequate symptom control had significantly more hospitalizations (12.0% vs 6.0%), ER visits (37.1% vs 22.6%), use of outpatient services (73.0% vs 60.7%), physician office visits (mean 11.0 vs 8.1), and prescription fills (mean 40.0 vs 26.7) annually (all p<. 01). Incremental costs associated with inadequate symptom control were $ 3,065 (2013 US dollars), and were driven by medical service costs ($ 2,391; 78%). Limitations: Study included US commercially insured patients only and inferred IBS-D status and inadequate symptom control from claims. Conclusions: Inadequate symptom control associated with available IBS-D therapies represents a significant economic burden for both payers and IBS-D patients.