[en] Background: Patients with clinically active Crohn's disease (CD), defined by a Crohn's Disease Activity Index (CDAI) > 150, may have normal Greactive protein (CRP) serum levels. In such cases, it is difficult to know whether these patients have really active disease or rather functional symptoms. This distinction is important to decide the most appropriate treatment. The aim of our work was to assess intestinal and colonic lesions in such patients and to look for biological markers potentially associated with endoscopic activity of the disease. Methods: We included 28 consecutive CD patients with CDAI >150 and a normal CRP level. These patients underwent a full colonoscopy with Crohn's Disease Endoscopy Index of Severity (CDEIS) calculation, fecal calprotectin, blood fibrinogen, acid a-I glycoprotein, and erythrocyte sedimentation rate measurement. The Harvey-Bradshaw score was also calculated. Serum ILI beta, IL6, IL8, sIL2R, and sTNFR2 were measured. Results: The median CDAI was 181 (151-485). Almost all (92.9%) these patients had endoscopic lesions, but the majority had only mild lesions (CDEIS : 6). No correlation was found between CDEIS and any of the clinical or biological markers. However, all the patients with significant endoscopic lesions (defined by a CDEIS >6) had previous surgical intestinal resection and lesions involving the anastomosis. Conclusions: Patients with elevated CDAT and normal CRP have only mild mucosal lesions of CD. Most significant lesions may be observed at the anastomosis and proximal to it in previously operated patients. None of the biological markers tested was associated with these endoscopic lesions.