We examined the influence of vessel size using an intention-to-treat approach in 259 patients who underwent stent implantation and in 257 patients who underwent balloon angioplasty alone in the BENESTENT trial. In the stented population, smaller vessel size was associated with a higher stent:vessel ratio, a greater relative gain and a greater subsequent loss index, and a higher risk of adverse cardiac events. In the balloon angioplasty population small vessel size conveyed an increased requirement for revascularization but did not increase the risk of procedural failure or myocardial infarction during follow-up. Logistic regression indicated that decreasing vessel size (as a continous variable) was associated with an increasing risk of a cardiac event for both the stent and balloon angioplasty populations.