Long-term antiplatelet treatment is associated with major bleeding. To determine the costs associated with major bleeding in patients treated with aspirin-based antiplatelet treatment for secondary prevention of vascular events without routine prescription of proton-pump inhibitors and to estimate the likely long-term savings from routine co-prescription. In a prospective population-based cohort study of TIA, ischemic stroke, and MI treated with antiplatelet drugs, we evaluated hospital care costs associated with bleed management during 10-year follow-up. Bleeding-associated costs were averaged across all patients. For upper GI-bleeds, mean costs were compared with the cost of routine co-prescription of proton-pump inhibitor. Among 3166 patients on antiplatelet therapy with 405 first bleeding events, the average cost of major bleeding was $13,093 (S.D. 20,501), with similar costs for upper GI bleeds and intracranial bleeds (p = 0.235). However, total costs among the 3166 patients were higher for upper GI bleeds ($1,158,385 vs. $740,123). Averaged across all patients, the 10-year cost of major bleeding was $838 (95%CI: 680-1007), $411 due to upper GI bleeding, the cost of which increased from $175 in those aged <75 years to $644 at age ≥75 years (p < 0.0001). The corresponding costs of routine life-long co-prescription of proton-pump inhibitor to those patients not on prior treatment were $85 (84-88) and $39 (38-42). In secondary prevention with aspirin-based antiplatelet treatment without routine proton-pump inhibitor use, the long-term costs of upper-GI bleeding at age ≥75 years are much higher than at younger age groups, and are at least 10-fold greater than the drug cost of routine co-prescription of proton-pump inhibitor.