Background: The relationship between plaque morphology, cerebral micro-embolic signals (MES) and platelet biomarkers in carotid stenosis in unclear. Methods: Data were combined from 2 prospective, multi-centre, observational studies (u2018Platelets And Carotid Stenosisu2019 and u2018HaEmostasis In carotid STenosisu2019) which assessed patients with recently symptomatic and asymptomatic moderate (u226550-69%) or severe (u226570-99%) carotid stenosis. Plaque morphology on Doppler ultrasound was graded with Gray-Scale Median (GSM) scoring. Bilateral transcranial Doppler ultrasound of middle cerebral arteries classified patients as u2018MES+veu2019 or u2018MES-veu2019. Full blood counts were analysed and whole-blood flow cytometry quantified platelet CD62P and CD63 expression, leucocyte-platelet complex formation and % reticulated platelets. This study was approved by the SJH/AMNCH Local Research Ethics Committee (Project/LREC Reference: 2011/31/02).Results: Data from 42 u2018recently symptomatic patientsu2019 (u22644 weeks of TIA/ischaemic stroke) were compared with those from 36 asymptomatic patients. There were no differences in median GSM scores between symptomatic and asymptomatic patients (25 vs. 30; P=0.31). Seven out of 42 (16.7%) symptomatic patients and none of the 36 asymptomatic patients were MES+ve (P=0.013). There were no differences in median GSM scores between MES+ve vs. MES-ve symptomatic patients (36 vs. 25; P=0.09). Symptomatic patients with echodense plaques (GSM scores u226525) had higher platelet counts (228 vs. 191 x109/L; P=0.02), neutrophil-platelet (3.3 vs. 2.7%; P=0.03), monocyte-platelet (6.3 vs. 4.55%; P=0.02) and lymphocyte-platelet complexes (2.91 vs. 2.53%; P=0.001) than u2018asymptomatic echodenseu2019 patients. Reticulated platelets were not increased in any group/subgroup.Discussion: Recently-symptomatic carotid stenosis patients with echodense plaques have enhanced platelet production/secretion/activation compared with their asymptomatic counterparts. Simultaneous assessment with neurovascular-imaging and platelet biomarkers enhances our understanding of the pathogenesis of symptoms and may aid risk-stratification and clinical decision making in carotid stenosis patients.