OBJECTIVES: When making reimbursement decisions, policy-makers in China need to consider the economic impact of the treatment, which is determined by both epidemiological factors and treatment costs.  In this study, we compare the total annual budget impact of different diseases of various treatment costs and prevalence rates.  METHODS: We considered six diseases in our analysis: hemophilia B, HIV, hypertension, non-small cell lung cancer (NSCLC), tuberculosis, and type 2 diabetes mellitus (T2DM).  These choices provided a sample of highly prevalent diseases (hypertension) and rare diseases (hemophilia B) as well as high cost (NSCLC) and low cost (type 2 diabetes) treatments.  The budget impact was calculated by multiplying the number of patients by the cost per patient.  The data sources for prevalence and cost were obtained using a search of previously published literature with the following criteria: in English, with abstract, published within the past ten years.  All costs were converted to USD using (1 USD = 6.07 RMB). RESULTS: China has a population of 1.3 billion, and the most common disease of our selection was hypertension (254 million) followed by T2DM (114 million), HIV (1.4 million), tuberculosis (1.3 million), NSCLC (515,000), and hemophilia B (4,887).   The annual per-patient-cost was highest for hemophilia B ($12,670) followed by NSCLC ($11,566), HIV ($2,242), tuberculosis ($724), hypertension ($367), and T2DM ($194).  The budget impact was highest for hypertension ($93 billion) followed by T2DM ($22 billion), NSCLC ($6 billion), HIV ($3 billion), tuberculosis ($900 million), and hemophilia B ($62 million).   CONCLUSIONS: When determining the economic impact of a treatment on a health system, payers need to consider both the cost of the treatment as well as the size of the patient population.  Though a rare disease may have high cost of treatment, its budget impact is relatively small because of the population size.