OBJECTIVE : We sought to investigate the efficacy of the proximal optimization technique (POT) on crossover stenting followed by side branch (SB) dilation under optical coherence tomography guidance in a multicenter registry study. RESULTS : A total of 135 bifurcation lesions in 134 patients were divided into POT (n = 52) and non-POT groups (n = 83). The POT was performed before SB dilatation (pre-POT; n = 26), finally (final-POT; n = 12), at both timing (re-POT; n = 13), and uncertain (n = 1). There were no significant intergroup differences in the success rate of guide wire re-crossing (GWR) into the optimal cell (72% vs. 65%), incidence of the link-free type in the configuration of the SB jailed struts (51% vs. 49%), or incomplete strut apposition at the bifurcation (13 ± 11% vs. 10 ± 9%). However, insufficient stent expansion close to the carina in the proximal main vessel (MV) due to inappropriate POT was likely to induce greater incomplete strut apposition (ISA) around the bifurcation. Only re-POT provided more symmetric proximal MV expansion, while pre- and final-POT did not. CONCLUSIONS : The POT did not provide the expected beneficial effects, such as reduction of ISA or more optimal GWR, under the OCT guidance. Wide stent expansion in the proximal MV induced by the POT increased the likelihood of achieving optimal GWR, whereas symmetric stent expansion was provided by re-POT.