OBJECTIVE To assess the clinical importance of on-treatment function testing of platelets in patients on aspirin after catheter-based vascular interventions. METHODS In 109 patients with symptomatic peripheral arterial disease (PAD) of the lower limbs, platelet function testing (adenosine diphosphate-, collagen- and epinephrine-induced aggregation using light transmission aggregometry) was performed before and at multiple time points up to 1 year after a percutaneous angioplasty. Using univariate mixture models and Box-Cox transformation to ensure normally distributed individual variances, we investigated if an intraindividual variability exists and if it has a consequence for clinical outcome. RESULTS Response to aspirin as measured by platelet aggregometry varies considerably over time in most patients. However, the intraindividual variance over time was not significantly correlated either with restenosis/reocclusion after 1 year or with adverse long-term outcome (occurrence of death for cardiovascular cause, stroke or myocardial infarction in up to 8 years follow-up). CONCLUSIONS Response to aspirin does not seem to have a role in determining long-term outcome in patients with symptomatic PAD. The fact that testing of platelet function at only one time point has reduced significance may have implications for all clinical settings in which aspirin is used for the prevention of thrombo-embolic events.