Methods.The newly described – multigene analysis test(DiBiCol) identifying 7 inflammatory bowel disease (IBD)-specific genes incolonic mucosal biopsy differentiating between ulcerative colitis (UC) and Crohn's disease (CD) with active inflammation – is a new addition to existingmethods with a higher stated sensitivity and specificity. Method biopsymaterial from 78 patients with a complicated course diagnosed as most probably UC in 38, CD in 18 and inflammatory bowel disease unclassified (IBDU) in 22 were investigated by DiBiCol. Results. DiBiCol showed a pattern consistent with CD in 13 patients with UC and led to change of diagnosis in 3 patients and a strong suggestion of CD in 8 patients. A total of 2 patients remained as UC. DiBiCol showed a pattern of UC in 4 patients of 18 with CD leading to a changing of diagnosis to UC in 3 patients, but the fourth remained as CD. In 22 patients with IBDU DiBiCol showed a pattern consistent with UC in 7 cases and with CD in 13 cases. A new evaluation 1 year after the DiBiCol allowed the assessment of clinical diagnosis in 10 patients confirmed in 9 of 10 patients by DiBiCol. In patients with acute flare of colitis the clinical diagnosis corresponded in 10 of 12 UC and in 5 of 6 CD cases. Summary. Adoptingthe DiBiCol test led to a change of the primary diagnosis in a significant number of patients with the initial diagnosis of UC and CD and suggested aclinically probable diagnosis in most of the patients with IBDU and in those with an acute flare of colitis.