Background: According to increasing use of ultrasound in the diagnosis of inguinal herniation, this study was designed to evaluate the cross-sectional area of the inguinal canal in patients with inguinal herniation and its increase with Valsalva maneuver. We also compared the obtained values with those of normal population. Methods: a cross-sectional study, 52 normal persons and 35 cases with inguinal hernia were assessed. The cross-sectional area of the inguinal canal was measured in all subjects and data was analyzed using Student’s t-test and Pearson's correlation tests in SPSS. Receiver operator characteristic (ROC) curves were traced to define cut-off points. Findings: Valsalva maneuver caused significantly greater increase in the cross-sectional area of the inguinal canal among patients than in the normal group. The cut-off point of the cross-sectional area of inguinal canal was 63.5 mm2 in neutral state and 72.5 mm2 with Valsalva maneuver (increase rate: 34 mm2). In the absence of Valsalva maneuver, a cross-sectional area of the inguinal canal of greater than 63.5 mm2 is predictive of inguinal hernia (with 91% sensitivity and 98% specificity). Otherwise, values greater than 72.5 mm2 will be predictive of inguinal hernia (with 100% sensitivity and 98% specificity). Inguinal hernia will also be suspected if Valsalva maneuver increases the cross-sectional area of the inguinal canal by more than 34 mm2 (with 91% sensitivity and 100% specificity). Conclusion: The following diagnostic criteria are suggested for diagnosis of inguinal hernia through ultrasound examination: the presence of bowel loop within the inguinal canal, a cross-sectional area of the inguinal canal > 63.5 mm2 without Valsalva maneuver and > 72.5 mm2 with Valsalva maneuver, an increase of > 34 mm2 in the cross-sectional area of the inguinal canal with Valsalva maneuver, and a > 0.5 cm movement of the spermatic cord with Valsalva maneuver. Keywords: Ultrasound, Inguinal hernia, Inguinal canal