Water enema as contrast material for examination of thecolon is the best method for measuring diameter of the lumen, wallthickness and showing regularity of the wall, characteristics oflesions and their relationship to surrounding structures (Palk, etal., 1997).Hydrosonography using 3D ultrasound can be performed inthe diagnosis of hollow organ pathology. This was found to bemore accurate than 2D ultrasound because of the multiple cut thatcan be made and also because of more accurate orientation(Esmat and Raziky, 2000)Aim of the work: This study is planned to evaluate andcompare, the role and the diagnostic efficacy of the 3Dhydrosonography of the colon in diagnosis of different colonicdiseases in comparison to colonoscopy.Patients and methods: This study was conducted on 20patients referred for colonoscopic examination to theGastrointestinal Endoscopy and Liver Unit, Kasr El Aini Hospital,Cairo University. Each patient was subjected to abdominalultrasonography, colonoscopy and 3D hydrocolonic sonography(3DHCS). The average duration of the 3DHCS was 20-30 minutes.All the patients completed the procedure successfully.Hydrocolonic sonography (HCS) was started by using 2Dexamination by the 3D probe till area of interest has been foundthen a 3D shot was taken for the expected lesion.Results: Eight masses were detected and gave the typicalpicture of malignancy (fixed to the wall, projects in the lumen and infiltrates the wall to different depth). Seven patients were found tohave sessile and pedunculated polyps. Two patients showedirregular thickened mucosal layer (>1.5 mm) and thickening of thewhole wall (> 4 mm) and the five layers were well demonstratedwith preserved wall stratification which is suggestive of being IBD.Histopathologies of these two cases were ulcerative colitis. Onepatient showed a thickened whole wall (1cm), with nodiscrimination of the colonic wall layers and narrow lumen withpoor distensability by water enema and alterations of the haustra.Also, it showed 5cm long stricture in the left part of the transversecolon where the bowel wall appeared thickened (1cm). This pictureby HCS was suggestive of malignancy, but proved to be CD byhistopathology. HCS did not show any significant abnormalities intwo mild ulcerative colitis cases.Conclusion: In our study the sensitivity and specificity of HCS indiagnosing colonic masses was extremely high. As well as, thesensitivity in detecting colonic non rectal polyps. HCS is not anaccurate tool in counting the polyp number. It seems likely thatHCS could not detect mild ulcerative colitis, but can be beneficialin the diagnosis of moderate to severe cases.