Enhanced platelet function, particularly in response to collagen, is a common occurrence in diabetes that increases the risk of cardiovascular disease. Ginkgo biloba extract is ingested primarily to improve mental focus but it also possesses a blood-thinning potential, which has not been well characterised. This study was designed to compare the effect of ingesting G. biloba extract on platelet aggregation in platelet-rich plasma (PRP) and prostanoid urinary excretion in healthy volunteers and subjects with Type 2 diabetes mellitus (T2DM). Before and after ingesting 120 mg of standardised G. biloba extract for 3 months, platelet aggregation was studied in PRP, and urinary metabolites of thromboxane B₂ (TXB₂) and prostacyclin (PGI₂) were measured. In healthy volunteers, the ingestion of G. biloba extract significantly increased fasting insulin and C-peptide and significantly reduced collagen but not platelet-activating factor (PAF)-mediated platelet aggregation, converting 21 of 28 subjects with [COL + /EPI + ] platelets to the [COL − /EPI + ] phenotype. This was accompanied by a reduction of 11-dehydro-TXB₂ and PGI₂. In the T2DM subjects, G. biloba ingestion did not affect pancreatic β-cell function but significantly reduced platelet aggregation, converting 16 of 19 [COL + /EPI + ] platelets to the [COL − /EPI + ] phenotype. Unlike the healthy volunteers, this was not accompanied by a reduced urinary prostanoid excretion.