Abstract Background Chronic diseases like inflammatory bowel diseases (IBD) can pose challenges to the self-concept of a patient. Illness identity (IID) describes a patient′s way to integrate a chronic illness into the self-concept distinguishing the dimensions rejection, engulfment, acceptance and enrichment. Associations between IID and psychological and physiological functioning have been shown in other chronic diseases, but haven’t been investigated in IBD. In this study, we focus on associations between IID and (i) psychosomatic well-being and (ii) response to biological therapy in patients with IBD. Methods Eighty-four patients with active IBD answered questionnaires assessing IID, anxiety, depression, childhood trauma, quality of life (QOL), fatigue and visceral sensitivity (VS.) before the beginning of treatment with biologicals. Response to therapy (n = 73) and changes in the reported outcomes (n = 46) were assessed 3–6 months later. Associations between IID types and QOL, anxiety, depression, childhood trauma, fatigue and VS were examined using Pearson′s correlation. Response to therapy was defined as i) reduction of Harvey Bradshaw-Index (HBI) of >/ = 3 points/Partial Mayo-Score (PMS) of 0–1 points (if HBI >5/PMS >1 at baseline) OR ii) decline of faecal calprotectin or CRP of at least 50% OR iii) confirmation of a significant decline of inflammation in endoscopy/ sonography/MRI. Logistic regression was conducted to examine associations between IID and response to therapy. Results IID-rejection was positively associated with anxiety (r = 0.23, p < 0.05), depression (r = 0.28, p < 0.01) and VS. (r = 0.43, p < 0.01). IID-engulfment was associated with lower QOL (r = -0.61, p < 0.01) and more fatigue (r = 0.45, p < 0.01), anxiety (r = 0.66, p < 0.01), depression (r = 0.63, p < 0.01) and VS. (r = 0.74 p < 0.01). In contrast, IID-acceptance was associated with higher QOL (r = 0.34, p < 0.01) and lower levels of fatigue (r = -0.34, p < 0.01), anxiety (r = -0.45, p < 0.01), depression (r = -0.33, p < 0.01), childhood trauma (r = -0.31, p < 0.01) and VS. (r = -0.52, p < 0.01). IID-enrichment was negatively associated with depression (r = -0.3, p < 0.01). Logistic regression indicated no association between IID and response to therapy. Conclusion This study is the first to examine the concept of IID in IBD patients. It supports previous findings regarding its association to QOL and psychological well-being in patients with chronic disorders. Contrary to our expectation, IID was not shown to influence treatment response in this cohort, which might be owed to the modest sample size. However, given the strong association between IID and QOL, future studies should investigate the potential of IID as a targetable characteristic in personalised holistic therapy.