OBJECTIVE Bile acid malabsorption (BAM) is a common cause of diarrhoea in Crohn's disease (CD) patients with ileal resection. BAM is usually diagnosed by selenium-labelled homotaurocholic acid test (75SeHCAT) but its availability is limited. Consequently, a large proportion of patients either remain undiagnosed or subject to empirical therapy. There is a paucity of studies examining the correlation between length of ileal resection and severity of BAM, which will be of use to clinicians with no recourse to diagnostic testing for BAM. METHODS We tested the correlation between length of resected ileum and percentage retention on 75SeHCAT of all CD patients with a prior surgical resection who underwent 75SeHCAT testing. Response to treatment with bile salt sequestrant and 75SeHCAT retention values was tested using Fisher's exact test. RESULTS A total of 91 patients were identified with a median age of 47 (IQR 21-80). The median length of resected ileum was 24 cm (range 15-165 cm) with a median of 1 resection (range 1-4). Overall, 88 patients (97%) had 75SeHCAT retention values of < 10% and 85 (93%) had retention of < 5%. There was a modest correlation between 75SeHCAT retention and length of ileal resection (Spearman's rho - 0.392, P = 0.0001). Data on response to treatment was available for 57 (63%) patients, of who 38 (67%) responded to bile salt sequestrant. There was no difference in 75SeHCAT retention values between responders and non-responders. CONCLUSIONS There was a modest correlation between length of ileal resection and severity of BAM as defined by 75SeHCAT retention values. Response to bile salt sequestrant therapy was not dependent on 75SeHCAT retention values.