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Data from geographic information systems (GIS) are important for developing input datasets for watershed models. However, the process used to translate GIS data into modelinput data can introduce errors. Although GIS data are routinely checked to assure their mapping accuracy, it is far less likely that the derived modelinput data are verified. The objective of this project was to assess GIS interfacegenerated data for the AGNPS watershed model by comparison to baseline data from a manually conducted field survey for the Horseshoe Creek watershed in Kansas. Multiple descriptors were used to assess agreement between datasets. Very good agreement was found for soil parameters (soil texture and erodibility), moderate agreement for landuse parameters (crop and management practice factors), and poor agreement for topographic parameters (slope and slope length). The absence of GIS data layers pertaining to management practices, such as contouring and terracing, reduced the agreement in landuse terms. Poor estimation of slope by the GIS interface model for larger cell sizes resulted in the poor agreement in topographic values. Issues related to appropriate cell sizes, generation of landmanagement practice GIS coverages, accuracy of GIS coverages, and accuracy of interface algorithms must be addressed by watershed modelers using GIS data.