Background: Portal hypertension occurs when the portal venous pressure exceeds 10mm Hg. Whatever the primary cause, the consequences of portal hypertension are similar. Liver cirrhosis is the commonest cause of portal hypertension. Because of its accessibility, lack of ionizing radiation and rapid assessment, sonography plays a major role in the assessment of portal hypertension. Even if the additional use of color and spectral Doppler improves the assessment of patients suspected of having portal hypertension, gray scale assessment of portal vein diameter is corner stone in the initial evaluation. Knowing the normal portal venous dimension in a specified population is so crucial. Methods: This is a prospective cross-sectional study done at Tikur Anbessa Specialized Hospital to sonographically determine the normal portal vein diameter. Data was collected from 502 patients on consecutive bases from May – September 2010. This includes 190 males and 312 females. Results: The mean portal vein diameter was 7.9 + 2mm with an increase in diameter with increase in age of the subject. Our study also revealed 21.5% increase in portal vein diameter with the phases of inspiration. Conclusion: This study has comparable results with studies done elsewhere so that it can be used as a baseline for future population based studies and clinical decision making.