Background <p>In humans, cats, and dogs, adrenal gland size appears slightly larger when measured by computed tomography (CT) compared to ultrasonography. However, CT measurement values have only been compared with ultrasound reference values retrospectively. This study aimed to directly compare CT and ultrasonographic measurement values of adrenal glands in dogs performed on the same day, under possible mimetic conditions. Thirty client-owned dogs without suspected adrenal disease scheduled for abdominal CT and ultrasound as part of diagnostic workup were enrolled. The maximum cranial and caudal pole diameter and length of both adrenal glands were measured using both modalities consecutively under the same anesthetic moment. Bland-Altman analysis of agreement between ultrasonographic and CT measurement values was performed. The results were also compared using the student’s t-test for normally distributed data and the Mann-Whitney rank sum test for non-normal distribution.</p> Results <p>For all investigated dimensions, the bias was positive, indicating that CT consistently produced larger measurement values than ultrasound.</p> <p>When stratification into different weight categories was applied, there was a significant difference in the measurement values of both poles of the left adrenal gland in all weight categories (P≤0.05). In contrast, for the cranial and caudal pole measurement values of the right adrenal gland, significant differences were found only in some weight categories. </p> Conclusions <p>The same imaging modality as originally used should be performed for patient follow-up. In larger dogs, greater discrepancies between ultrasonographic and CT acquired measurement values may be expected. When comparing measurement values acquired by CT and US, the information on the caudal pole size may be expected to be less variable than the cranial pole. </p>