BACKGROUND: Renal artery stent restenosis remains a significant impediment that in part is attributed to suboptimal stent deployment. We tested the hypothesis that optimal stent deployment during renal artery interventions can be achieved using the Metricath (MC) system, a balloon-catheter sizing device. METHODS: The MC low-pressure balloon derives accurate vessel lumen dimensions from the three-dimensional reconstruction of volume of fluid and pressure within the inflated balloon. We systematically compared the final visual assessment of renal artery intervention with a subsequent MC minimal lumen diameter (MLD) in patients undergoing renal artery stenting. RESULTS: Sixteen patients underwent angioplasty and stenting of 20 renal artery lesions. MC guidance resulted in adjunctive intervention in 90% of lesions, increasing MLD from 4.40 ± 0.77 mm before to 5.17 ± 0.82 mm (p < 0.001) after adjunctive intervention. The MC MLD to the angiographic reference vessel diameter improved from 77.4 ± 15.2% to 91.2 ± 17.5% (p < 0.001), and the MC MLD to the nominal stent diameter improved from 76.2 ± 7.1% to 90.0 ± 9.4% (p < 0.001) after adjunctive intervention. Stent expansion was more pronounced at its distal site compared to the lesion site where the postinterventional distal stent MLD was 5.52 ± 0.93 mm (p = 0.23), and the lesion MLD was 5.17 ± 0.82 (p = 0.001) compared to a nominal stent diameter of 5.78 ± 0.88 mm. An MC MLD-to- nominal stent diameter ratio greater than or equal to ≥85% occurred in 10% of lesions before adjunctive dilatation and in 65% of lesions after adjunctive balloon post dilatation. CONCLUSIONS: MC guidance during renal interventions revealed a large proportion of underdeployed stents that were further optimized by adjunctive intervention.