Between 1974 and 1992, we perform 3,054 colonoscopies for diagnosis in 2,770 patients, both of sexes, between the ages of 1 and 101 yr, most of them over the fifth decade of life. In 300 procedures the bowel cleansing was made with the standard method of liquid diet and enemas, and in the other 2,754 with the oral administration of saline solution 9% with optimal results. We get the sedation of patients with the intravenous administration of diazepam 10mg, or pethidine 50 mg, or midazolam 2.5 to 5 mg, and in children with ketamine and the anesthesiologist assistance. In 95% of the procedures we can see the cecum and the ileum; the diagnosis was abnormal in 52.78% of cases, normal in 45.20%, and insufficient in 02.02% specially for a bad cleansing of the bowel. In the abnormal group, the most frequent diseases we diagnose were: polyps, cancer, diverticular disease, and specific inflammatory disease of the bowel like TBC, radiation proctosigmoiditis, amebiasis, and non-specific bowel disease: "colitis", ulcerative proctocolitis, erosive colitis, and Crohn's disease. Colonoscopy is a very important method for diagnosis of colon diseases, alone or complementary of double contrast X-ray of the colon.