OBJECTIVES:  Biosimilar (B) uptake in Belgium is closely related to the hospital financing system. B are mainly distributed through hospitals and bilateral discount negotiations between the hospital pharmacy and company exist. This budget impact analysis (BIA) estimates the influence of different B uptake percentages & discount rates from a hospital perspective (Belgium). METHODS: The current usage data 2015 (only originator (O); no B uptake) of infliximab, epoetin alfa, filgrastim and follitropine alfa in the tertiary care Ghent University Hospital for all authorized indications were retrieved. Potential discount%, future price reductions for both B & O and potential fluctuation in consumption are analyzed for 3 uptake scenarios: newly diagnosed patients (de novo), 20% and 100% switch of patients. The BIA uses the official Belgian tariff unit prices (NIHDI). A discount difference (in favour of B) of 10% is used for epoetin alfa and follitropine alfa; 20% for infliximab; 40% for filgrastim. Key variables (discount%, price, consumption) were tested in deterministic univariate sensitivity analyses [MIN, MAX]. Time horizon is 5 years. RESULTS: Infliximab showed the highest cumulative savings with de novo, 20% and 100% scenario of resp. €686.896,45 [€171.724,11- €1.373.792,90], €763.541,59 [€190.885,40 - €1.527.083,19] and €3.817.707,97 [€954.426,99 - €7.635.415,93], followed by filgrastim with resp. savings of €420.706,24 [€-29.213,72 € - €841.412,49], €105.637,35 [€-7.335,75 - €211.274,71] and €528.186,77 [€-36.678,73 - €1.056.373,54]. Follitropine alfa savings were €68.443,54 [€-12.271,96 - €136.887,09], €19.367,16 [€-3.472,54 - €38.734,32] and €96.835,80 [€-17.362,71 - €193.671,60] and epoetin alfa: €22.495,20 [€-1.649,00 - €44.990,40], €7.380,68 [€-541,36 - €14.761,36] and €36.903,39 [€-2.706,82 - €73.806,78]. Savings became in favour of O (negative MIN) if O-discount% increased 5% (filgrastim), 20% (follitropine alfa, epoetin alfa) above B-discount%. Increased consumption dominated the MAX values. CONCLUSIONS: All base-case simulated scenarios were in favour of the biosimilar. Only discount variation inverted the results pro originator.