A polymorphism of glycoprotein IIb/IIIa has been associated with myocardial infarction and restenosis after percutaneous coronary intervention. The influence on outcome and the interaction of the Pl(A1) genotype with classic risk factors for coronary artery disease (CAD) were characterized in patients with chronic CAD followed prospectively for 3 years. Pl(A1) genotypes were assessed in 592 patients enrolled in the Medical, Angioplasty, or Surgery Study II, a randomized trial comparing treatments for patients with CAD and preserved left ventricular function. The incidence of the composite end point of cardiac death, myocardial infarction, and refractory angina requiring revascularization were determined in each genotype group. Risk was assessed with the Cox proportional-hazards model. The clinical characteristics and treatment of each genotype were similar. Although the composite end point tended to be more common in patients with the Pl(A2) allele, only smokers with the Pl(A2) allele had a significantly increased incidence of the composite end point (p = 0.01). Moreover, a 2.2-fold increased risk was apparent in smokers with the Pl(A2) allele (p = 0.03). Thus, taken together, these data provide support for the interaction effect between smoking and the Pl(A1) gene variant. Smokers with the Pl(A2) polymorphism of platelet glycoprotein IIIa are at greater risk for subsequent cardiac events in stable coronary disease.