-Background -Crohn's disease accompanied by nonspecific or idiopathic ulcerative proctocolitis corresponds to a condition called intestinal inflammatory disease. The immunoexpression of cyclooxygenase 2 (COX-2) in Crohn's disease becomes more marked with progression of the disease and the presence of wild-type p53 suppresses the transcription of COX-2. Aims -To investigate the immunoexpression of cyclooxygenase 1 (COX-1), COX-2 and p53 in Crohn's ileocolitis and to correlated this expression with clinical and histopathological parameters. Methods -Forty-five cases of Crohn's disease, 16 cases of actinic colitis (diseased-control group) and 11 cases without a history of intestinal disease (normal control group) were studied. Hematoxylin-eosin-stained sections were submitted to histopathological analysis and the immunohistochemical expression of COX-1, COX-2 and p53 was evaluated by the streptavidin-biotin-peroxidase method. Results -Sixty percent of the Crohn's disease patients were women and 40% were men, with 75.5% whites and 25.5% non-whites. The disease involved the terminal ileum in 44.5% of cases, ileum in 33.3%, colon in 20% and duodenum-ileum in 2.2%. A significant association was observed between COX-2 immunoreactivity and age ≤40 years. Histopathological analysis of Crohn's disease samples showed mild or moderate crypt distortion (57.8% and 35.6% of cases), atrophy (6.6%), mild, moderate and marked chronic inflammation (46.7%, 26.7% and 20%), acute inflammatory activity (93.3%), ulceration (24.4%), mucin depletion (37.8%), Paneth's cells (24.4%), intraepithelial lymphocytes (93.3%), and subepithelial collagen (6.7%). In the CD group, COX-1 immunoreactivity in epithelial and inflammatory cells was observed in 26.7% and 22.2% of cases, respectively.