The changes in the system of healthcare reimbursement by public insurance agencies have gradually reduced public coverage of sickness risk. The system leaves the insured to bear expenses that can prove significant for long and costly illnesses-sometimes even when the insured are eligible for payment exemptions because of long-term conditions. Although this situation has made supplementary insurance a necessity, 7% of the French population lacks such coverage. We simulate a reform of compulsory sickness insurance that would put an annual cap on copayments for primary healthcare, financed by the introduction of annual deductibles. We assess the reform using microsimulations applied to data from the 2003 Health and Medical Care Survey, matched against reimbursement data from the National Health Insurance Inter-Plan Information System (SNIIRAM). The large sample size enables us to produce detailed simulations of patients' financial contributions to healthcare expenditures under different scenarios. We can thus evaluate the various possible reforms of the healthcare reimbursement system in terms of fairness, financial-risk coverage, and political feasibility. The annual cap notably offers a genuine improvement in coverage for patients with heavy expenses, giving them better protection against sickness risk and catastrophic-expenditure risk. We also find that the reimbursement system becomes fairer when the cap is proportional to patients' income.