OBJECTIVES: The SF-36, a generic health-related quality of life measure, comprises 8 domains (Ware 2000) for which physical and mental component summaries (PCS and MCS) can be derived (Ware, Kosinski 2001). Until now, no MID for the SF-36 domains and summary scores have been reported for patients with active Crohn's disease (CD). Our aims were to determine the MID for SF-36 using data from the PRECiSE 1 trial (Sandborn et al. 2006), and to use these MIDs for the interpretation of results from the PRECiSE 2 trial investigating certolizumab pegol maintenance treatment (Schreiber et al. 2005). METHODS: SF-36 MIDs were estimated by anchor-based methods using known meaningful changes in reference measures (Inflammatory Bowel Disease Questionnaire [IBDQ] and CD Activity Index [CDAI]). The a priori approach was to select the SF-36 MID according to the most correlated anchor. Agreement of the anchor-derived MIDs with results obtained using Standardised Effect Sizes, Standard Errors of Measurement and Standard Errors of the Difference was also evaluated. RESULTS: The two anchors gave similar values of meaningful changes. The IBDQ, which correlated most closely to SF-36 score changes, was selected to derive the SF-36 MIDs. Results obtained with other methods were in agreement with these derived MIDs and were representative of small to moderate changes (effect sizes ranging from 0.2 to 0.5). Based on these calculations, it was shown that a significantly higher proportion of patients showed a clinically meaningful response in the SF-36 PCS and MCS after certolizumab pegol maintenance treatment compared to patients receiving placebo. CONCLUSION: A multi-faceted approach to determining MIDs for the SF-36 domain and summary scores was investigated for the first time in patients with active CD. This enables a more meaningful interpretation of SF-36 scores in CD patients.