Objectives Intravascular ultrasound (IVUS) was performed to investigate the impact of kissing balloon inflation (KBI) on the main vessel (MV) stent volume, area, and symmetry after side-branch (SB) dilation in patients with coronary bifurcation lesions (CBL). Background It remains controversial whether KBI would restore the MV stent area and symmetry loss after SB dilation. Methods A total of 88 serial IVUS examinations of the MV were performed after MV angioplasty, MV stenting, SB dilation, and KBI in 22 patients with CBL. The MV stent was divided into proximal, bifurcation, and distal segments; the stent volume index (SVI), minimal stent area (MSA), stent symmetry index (SSI), and external elastic membrane (EEM) volume index were measured in 198 stent segments and compared after MV stenting, SB dilation, and KBI. Results In the bifurcation segment, SVI, MSA, and SSI were significantly smaller after SB dilation than after MV stenting and KBI (SVI was 6.10 ± 1.50 mm3/mm vs. 6.68 ± 1.60 mm3/mm and 6.57 ± 1.60 mm3/mm, respectively, p < 0.05; MSA was 5.15 ± 1.30 mm2 vs. 6.08 ± 1.40 mm2 and 5.86 ± 1.50 mm2, respectively, p < 0.05; and SSI was 0.78 ± 0.02 mm2 vs. 0.87 ± 0.03 mm2 and 0.84 ± 0.03 mm2, respectively, p < 0.05). KBI restored the MV SVI, MSA, and SSI after SB dilation. In the proximal segment, SVI, MSA, and EEM volume index were significantly larger, but SSI was smaller after KBI than after MV stenting and SB dilation. In the distal segment, neither SB dilation nor KBI had a significant impact on the MV stent volume or symmetry. Conclusions This is the first comprehensive volumetric IVUS analysis of CBL, to our knowledge, demonstrating that KBI restores the MV stent volume, area, and symmetry loss after SB dilation in the bifurcation segment, and induces asymmetric stent expansion in the proximal segment. © 2013 by the American College of Cardiology Foundation.