Despite being proposed 4 years ago, there has been no independent validation study of the Rome IV criteria for IBS. We assessed their performance for the diagnosis of IBS in secondary care and compared them with the previous iteration, the Rome III criteria.We collected complete symptom data from consecutive adult patients with suspected IBS referred to a single UK clinic. All subjects underwent relatively standardised workup, with assessors blinded to symptom status. The reference standard used to confirm IBS was the presence of lower abdominal pain or discomfort in association with altered stool form or frequency, in a patient with no evidence of organic gastrointestinal disease after investigation. Sensitivity, specificity and positive and negative likelihood ratios (LRs), with 95% CIs, were calculated for each of the diagnostic criteria.The level of agreement between the Rome IV and Rome III criteria was good (kappa=0.65). Compared with the reference standard, sensitivity and specificity of the Rome IV criteria in 572 patients (431 (75.3%) women, mean age 36.5 years) were 82.4% and 82.9%, respectively. Positive and negative LRs for the Rome IV criteria were 4.82 (95% CI 3.30 to 7.28) and 0.21 (95% CI 0.17 to 0.26), respectively. The Rome IV criteria performed best in those with IBS with constipation or mixed bowel habits. In 471 patients (350 (74.3%) women, mean age 36.7 years), compared with the reference standard, the sensitivity and specificity of the Rome III criteria were 85.8% and 65.0%; positive and negative LRs were 2.45 (95% CI 1.90 to 3.27) and 0.22 (0.16 to 0.29), respectively. Incorporating mood and extraintestinal symptom reporting into diagnostic criteria did not improve their performance significantly.The Rome IV criteria performed significantly better than the Rome III criteria in diagnosing IBS in this single centre secondary care study, although the clinical relevance of this is uncertain.