A gross margin (GM) model is being developed to predict the on-farm financial impact of ovine Johne's disease (OJD) for a range of wool and sheep-meat enterprises and disease scenarios within Australia. Individual GM budgets will be developed for Merino fine (19μm), medium (21μm) and strong (23μm) wool enterprises as well as for 1st and 2nd cross lamb production. Disease scenarios include non-infected, infected (status quo) and infected (vaccination). The infected scenario reflects low (<3%), medium (3 to < 7%) and high (7% and greater) OJD mortalities. The status quo scenario assumes no control and the vaccination scenario simulates a reduction in OJD mortalities, based on Australian mortality and vaccine research. Sheep numbers are modified for each enterprise to reflect mortality throughout the year. Income accounts for sales of wool, sheep and fodder while variable costs include sheep health, wool and stock selling, supplementary feed, pasture, weeds and pests and the cost of replacement sheep. Commodity prices are based on five-year median prices obtained from the NSW Dept. of Primary Industries. A discount value is applied to account for debt levels and capital effects. The model will estimate changes in profits due to increased mortalities, as a result of OJD, and the cost of control through the use of Gudair™. Gross margins are reported as total, per ewe or wether, per dry sheep equivalent (DSE) and per hectare (ha). The cost of OJD is reported as reduced wool income and sheep sales whereas the benefits of control are reported as increased wool income and sheep sales. The output will be presented as net present value (NPV) at 5, 10, 15 and 20-year intervals. This paper will present the model and its outputs, an important tool for determining the financial impact of OJD on individual farms and developing cost effective strategies for disease control and management.