Aim To investigate the value of ultrasound in the diagnosis of congenital internal carotid artery hypoplasia (CICAH). Methods Patients diagnosed with CICAH by ultrasound in Baotou Central Hospital, Inner Mongolia from July 2022 to December 2023 were retrospectively collected. The general data, ultrasound and imaging data of all patients were recorded. Results Among the 25 317 carotid artery ultrasonography subjects, 13 patients were diagnosed as CICAH. The ultrasonic detection rate of CICAH was 0.051%. The 13 cases of CICAH included 11 cases of unilateral internal carotid artery hypoplasia and 2 cases of bilateral internal carotid artery hypoplasia. CT scan of carotid canal confirmed that all 13 cases of internal carotid artery hypoplasia were unilateral lesions, among which 2 cases of unilateral lesions were misdiagnosed as bilateral lesions by ultrasound, with a misdiagnosis rate of 15%. Taking carotid canal dysplasia as the gold standard, ROC curve was plotted to evaluate the diagnostic value of ultrasound in CICAH. The area under the curve (AUC) was 0.941, and the optimal diagnostic threshold value of CICAH was 3.2 mm, sensitivity was 100%, and specificity was 85%. The consistency test between ultrasonic examination and gold standard test method for CT scanning of carotid artery canal showed that Kappa value was 0.846. Conclusion Ultrasound has a high diagnostic value in the diagnosis of CICAH, and can be used as the first choice of clinical examination.