The histopathologic diagnosis of inflammation is common in colorectal biopsies but is of limited value, if not further specified. We reviewed 280 endoscopic colorectal biopsy specimens for nonneoplastic disease from 100 consecutive patients in order to assess (a) the frequency of inflammation in excess of the physiologic infiltrate, (b) the frequency with which the cause of the inflammation could be specified, and (c) the interobserver variability in diagnosing inflammation. Based on the reviewers' impression, each case was classified into one of three categories: (I) normal or nonspecific change, (II) nonspecific inflammation, and (III) inflammation suggestive or diagnostic of specific cause. Inflammation was diagnosed in 68% of cases. The majority of these cases (75%) showed features typically associated with specific types of colitis, including Crohn's disease (n = 16), ulcerative colitis (n = 13), inflammatory bowel disease not otherwise specified (n = 5), infectious colitis (n = 6), ischemic colitis (n = 4), solitary rectal ulcer syndrome (n = 3), radiation colitis (n = 2), and lymphocytic colitis (n = 2). Interobserver variability was greatest in biopsy specimens interpreted by the reviewers as normal or showing nonspecific changes, most of which had been diagnosed as mild inflammation by the original pathologists. Etiologic classification of colitis was lacking in 59% of the cases interpreted by the reviewers as suggestive or diagnostic of a specific cause. We conclude that (a) the majority of colorectal biopsy specimens from patients with nonneoplastic disease in this series show inflammation, (b) the majority of such cases allow a specific cause of colitis to be suggested or firmly diagnosed, and (c) pathologists tend to overdiagnose the physiologic inflammatory infiltrate as evidence of colitis and underdiagnose specific etiologic types of colitis.