OBJECTIVES: Given the lack of specific ICD-9 codes, no definitive method exists for identifying irritable bowel syndrome with constipation (IBS-C) and chronic constipation (CC) patients in administrative claims. This study compared patients identified as having IBS-C and CC through claims-based algorithms with modified Rome III criteria and patient-reported physician diagnoses. METHODS: Consenting patients aged ≥18 years identified from the HealthCore Integrated Research Database as having IBS-C (≥1 IBS claim and ≥2 constipation claims or ≥1 constipation claim and ≥1 constipation-related pharmacy claim) or CC (≥2 constipation claims ≥90 days apart or ≥1 constipation claim and ≥1 constipation-related pharmacy claim ≥90 days apart and no IBS claims) completed a cross-sectional survey that included questions pertaining to IBS-C/CC symptoms based on modified Rome III criteria and patient self-report of IBS-C and CC physician diagnoses to confirm claims-based diagnoses. RESULTS: Among 236 claims-based IBS-C patients, 22% met Rome III IBS-C criteria and 43% reported being told by a physician they had IBS-C. In addition, 33% of claims-based IBS-C patients reported being told by a physician they had CC. Among 456 claims-based CC patients, 27% met Rome III CC criteria and 39% reported being told by a physician they had CC.  However, 38% of claims-based CC patients met Rome III criteria for IBS-C and 18% reported being told they had IBS-C. Patients who did and did not meet Rome III criteria had similar demographic and clinical characteristics. CONCLUSIONS: A majority of patients identified as having IBS-C and CC via claims did not meet Rome III criteria. There was greater agreement between claims-based criteria and patient-reported physician diagnoses than Rome criteria. Our findings suggest that patients identified through claims may have been asymptomatic at the time of the survey, and those identified as CC patients may be IBS-C patients who never received an IBS claim.