AIM:To estimate the prevalence of colorectal cancer (CRC) in patients with long lasting colonic symptoms undergoing total colonoscopy;and to establish clinical features predicting its occurrence.METIHODS:This prospective study was carried out in Imam Hospital,Tabriz University of medical sciences,Iran.Continuous patients with long lasting lower gastrointestinal tract symptoms who had the criteria of a colonoscopy were included.The endoscopist visualized the caecum documented by a photo and/or a specimen from terminal ileum.RESULTS:Four hundred and eighty consecutive symptomatic patients [mean age (SD):42.73 (16.21)]were included.The prevalence of colorectal neoplasia was 15.3%(34 subjects) and 37.7% (181 subjects)had a completely normal colon.Adenomatous polyps were detected in 56 (11.7%) patients,in 12.3% of men and 10.9% of women.The mean age of the patients with a polyp was significantly higher than the others (49.53±14.16 vs 41.85±16.26,P=0.001).Most of the adenomatous polyps were left sided and tubular;only 22.5% of polyps were more than 10 mm.Cancer was detected in 16 (3.6%) of our study population,which was mostly right sided (57.2%).The mean age of patients with cancer was significantly higher than the others (60.25±8.26 vs 42.13±16.08,P＜0.005) and higher than patients with polyps[60.25 (8.26) vs 49.53 (1.91) (P＜0.0005)].None of the symptoms (diarrhea,abdominal pain,rectal bleeding,constipation,altering diarrhea and constipation,history of cancer,known irritable bowel disease,history of polyp and fissure or family history of cancer) were predictors for cancer or polyps,but the age of the patient and unexplained anemia independently predicted cancer.CONCLUSION:Less advanced patterns and smaller sizes of adenomas in Iran is compatible with other data from Asia and the Middle East,but in contrast to western countries.Prevalence of colonic neoplasia in our community seems to be lower than that in western population.Colonic symptoms are not predictors for polyps or cancer but unexplained anemia and elder age can predict CRC.