This supplementary appendix provides additional information to the main article by Schultz et al. on thrombosis and thrombocytopenia following ChAdOx1 nCoV-19 vaccination. It includes detailed methods for heparin-induced multiple electrode aggregometry (HIMEA) testing, which measures platelet aggregation in response to heparin. The appendix also presents brain CT scans and angiography images from Case 5, showing significant cerebral venous sinus thrombosis and the successful outcome of endovascular thrombectomy. Additionally, it includes a figure illustrating the serial dilution of patient sera in an IgG anti-PF4/polyanion ELISA assay, which is used to detect specific antibodies. The appendix concludes with a reference to a study on endovascular treatment for cerebral venous sinus thrombosis.This supplementary appendix provides additional information to the main article by Schultz et al. on thrombosis and thrombocytopenia following ChAdOx1 nCoV-19 vaccination. It includes detailed methods for heparin-induced multiple electrode aggregometry (HIMEA) testing, which measures platelet aggregation in response to heparin. The appendix also presents brain CT scans and angiography images from Case 5, showing significant cerebral venous sinus thrombosis and the successful outcome of endovascular thrombectomy. Additionally, it includes a figure illustrating the serial dilution of patient sera in an IgG anti-PF4/polyanion ELISA assay, which is used to detect specific antibodies. The appendix concludes with a reference to a study on endovascular treatment for cerebral venous sinus thrombosis.