The correct arterial cannula size for percutaneous femoral venoarterial extracorporeal membrane oxygenation (VA-ECMO) cannulation is imperative for adequate circulatory support. We aimed to describe the relationship between cannula size, predicted arterial size, and vascular complications. Here, we present a single-center cohort of patients who underwent percutaneous femoral VA-ECMO cannulation. A formula using height and body mass index was used to predict the estimated common femoral artery (CFA) diameter and compared it to the cannula size used. The primary endpoint was major vascular complications. Receiver Operating Characteristic (ROC) curve was used to determine the cutoff point for significant cannula size discrepancy (≥2.7 Fr greater than predicted). Twenty-five patients were included, with a median predicted CFA diameter of 5.4mm (16.2 Fr), 1.9 Fr lower than the chosen cannula. Eight patients (32%) had a significant cannula discrepancy with more vascular complications (p = 0.039). ROC analysis confirmed a moderate correlation between cannula discrepancy and major vascular complications (area under the curve [AUC] 0.640, sensitivity of 67%; specificity of 84%) and overall vascular complications (AUC 0.662, sensitivity of 63%; specificity of 88%). Thus, the use of arterial cannulas for percutaneous VA-ECMO that are ≥2.7 Fr larger than the estimated CFA appears to be related to a higher risk of overall vascular complications. The estimated arterial diameter should be considered when selecting the arterial cannula size.