Technical Abstract: The long term performance and economics of forage systems are best compared using a simulation model of the dairy farm called DAFOSYM. Simulations illustrate that either alfalfa or corn silages provide good forages for dairy farms in the Midwest. Although there are not large economic differences when using various portions of alfalfa and corn silage, a mix of one third to one half corn silage may be preferred. This mix reduces economic risk, spreads labor requirements more uniformly throughout the production season and it provides the best long term nutrient balance for the whole farm. When expanding silage storage, bagged silage may be the most economical option, but the inconvenience of handling and disposal of plastic bags must be considered. Dry hay systems can be an economical forage system, particularly for small farms. For Midwest farmers who prefer to use total mixed ration feeding, systems which predominately use silages are most convenient and most economical. For those interested in further analysis and comparison of dairy systems, a Windows version of DAFOSYM is available from the home page of the U.S. Dairy Forage Research Center (http://www.dfrc.wisc.edu).