The impact of type of balloon such as noncompliant (NC; Quantum) or semicompliant (SC; Maverick(2)) used after stent dilation on optimal stent expansion (OSE) has not been established for drug-eluting stents (DESs). We conducted a prospective multicenter, randomized study to compare NC with SC balloons after stent balloon dilatation. A total of 301 patients (127 men, 83 women, 62 +/- 9 years of age) treated with a DES (sirolimus-eluting stent [SES], n = 152; paclitaxel-eluting stent, n = 149) were included. OSE followed the definition of the Multicenter Ultrasound Stenting in Coronaries (MUSIC) study. The primary end point was the incidence of OSE using intravascular ultrasound according to type of balloon. Baseline characteristics of each group showed no significant differences. OSE in the SC balloon group was achieved at higher rates than the NC balloon group (53 +/- 35%, vs 73 +/- 48%, p = 0.022 in all stents; 25 +/- 33%, vs 36, 48%, p = 0.051 in SESs). However, any differences in the achievement of OSE between the NC and SC balloon groups were not present in paclitaxel-eluting stents. In conclusion, despite postadjuvant balloon inflations with high pressures, underexpansion of the DES was seen commonly. Between the 2 types of balloon for adjuvant dilation after DES implantation, same-size SC balloons could be more useful for obtaining OSE than NC balloons, especially in SESs.