PURPOSE:It has been documented that Crohn's disease affects anorectal function when anorectal manifestations of the disease are present. The aim of this study was to investigate whether the presence of histologic lesions in rectal biopsy affected anorectal motility in patients with Crohn's disease but no evidence of macroscopic anorectal involvement.METHODS:Forty‐one patients with documented Crohn's disease were included in the study. Twenty‐one of them had no endoscopic or histologic lesions in the rectum, and 20 patients had a positive histology for Crohn's disease on rectal biopsy, with or without macroscopic or endoscopic involvement of the anorectum. All patients underwent a standard anorectal manometry, with an eight‐channel, water‐perfused catheter.RESULTS:Patients with positive rectal biopsy but no evidence of endoscopic rectal involvement had lower anal resting and squeeze pressures (76±16 standard deviationvs.86±19 standard deviationP=0.002; 152±56 standard deviationvs.192±52 standard deviationP<0.001, respectively), and a lower sphincter and high‐pressure zone length (2.8±0.8 standard deviationvs.3.2±0.8 standard deviationP=0.006; 1.7±0.6 standard deviationvs.2±0.6 standard deviationP=0.005, respectively) compared with patients with negative rectal histology. Also, slow and ultra slow wave amplitude and ultra slow wave frequency were significantly lower (10±6 standard deviationvs.13±7 standard deviationP=0.04; 17±16 standard deviationvs.34±24 SDP=0.004; 0.9±0.8 standard deviationvs.1.3±0.6 standard deviationP=0.05, respectively), rectal sensation more affected, and rectal compliance significantly reduced (7.4±1 standard deviationvs.11.1±2.2 standard deviationP<0.001) in the former group of patients. Simultaneous presence of endoscopic and histologic lesions in the rectum was associated with further impairment of the anorectal function.CONCLUSION:Microscopic presence alone of Crohn's disease in the rectum appears to induce anorectal motility disorders. The synchronous presence of endoscopic rectal and macroscopic anal involvement is associated with further deterioration of anorectal function.