Vegetated treatment systems (VTS) are designed to control runoff from beef feedlots. A VTS consists of a solids settling basin followed by either a vegetated treatment area (VTA) or a vegetated infiltration basin (VIB) followed by a VTA. Two computer models were developed at Iowa State University (ISU) to simulate traditional containment, a VTS with a settling basin and a VTA, and a VTS with a settling basin, VIB, and VTA. The models predict runoff volume and nutrient mass entering and leaving the system for a given design and specific weather conditions. In this paper, the monitored performance of four feedlot VTSs in Iowa is compared to the performance predicted by each site model run. These sites are undergoing extensive monitoring to determine the mass of nutrients discharged from each system component. Weather data including maximum temperature, minimum temperature and precipitation are also continuously recorded. System component discharge data collected at each site is compared to data generated by the model using site specific weather data for model calibration purposes. Comparisons of modeled versus monitored system performance indicate that the VTS models currently under predict discharge from the VTAs at all four sites. The VTS models also under predicted the VIB performance for both of the VIB sites. While the measured and monitored flow volumes from the SSB matched relatively well, the nutrient concentration released from the SSB was much higher than the concentration predicted by the VTS models.