Objective: Conventional two-dimensional ultrasound (2D-US) has been the recommended and preferred modality for the diagnosis and surveillance of abdominal aortic aneurysms (AAAs). Measurement of the aneurysm diameter using three-dimensional ultrasound (3D-US) has shown promising results in a research setting, improving agreement and reproducibility. However, studies evaluating 3D-US in a clinical context are lacking, which could hinder the optimal usage of this new modality. In the present study, we investigated the clinical value of 3D-US for AAA surveillance compared with the current standard 2D-US examination. Methods: Data from 126 patients with infrarenal AAAs <50 mm and 55 mm (female and male, respectively) were available for analysis. Eligibility was determined using the standard 2D-US anteroposterior (AP) diameter with a dual-plane technique. All the patients had subsequently undergone additional 3D-US and computed tomography angiography (CTA). Using CTA as the reference standard, the maximal standard 2D-US AP diameter was compared with that from 3D-US. Results: All 126 AAAs were, per the inclusion criteria, small, with no intervention indicated. With the addition of 3D-US imaging to the 2D-US–based surveillance program, the AAA diameter threshold (50 and 55 mm) was exceeded for 31 of the 126 patients (25%). These 31 patients were withdrawn from the present study and referred for treatment planning. Compared with the CTA AP diameter (mean, 49 ± 7.2 mm), the mean 3D-US AP diameter (mean, 49 ± 6.7 mm) was significantly more accurate than the standard mean 2D-US AP diameter (45 ± 6.2 mm; kappa value, 0.86 ± 0.05; 95% confidence interval, 0.76-0.96; kappa value, 0.01 ± 0.04; 95% confidence interval, −0.05 to 0.09, respectively). Conclusions: For clinical use, the AAA diameter assessment using 3D-US was significantly more accurate than that with 2D-US and can substantially change the clinical management, from surveillance to operative treatment, for approximately one fourth of patients with an AAA. Further studies evaluating the clinical consequences of the 2D to 3D paradigm shift in AAA diagnostics are warranted, including sensitivity, specificity, agreement, and reproducibility estimation.