Discharge estimations at certain cross sections of streams are very important for hydrologic studies especially for designs. In this study, it is aimed to determine regional mathematical equations that represent annual and monthly average discharges at desired locations using basin characteristics obtained with Geographical Information Systems (GIS) techniques and regression analysis. Study area covers three river basins, which are Gediz, K&uuml / &ccedil / &uuml / k Menderes and B&uuml / y&uuml / k Menderes. The data used are Digital Elevation Model (DEM), monthly average discharges observed at stream gauging stations and monthly total precipitation data from the precipitation observation stations in the study area. Stream networks are delineated from DEM using a GIS software. The basin parameters obtained from DEM are drainage area, total river length, main channel slope, main channel length and mean basin slope. Precipitation amount is also included in the analyses as the sixth parameter to improve the results. Using these parameters annual and monthly average discharge equations are determined and the best equation for each month is found based on the adjusted coefficient of determination values and stepwise regression analysis. Three models, each representing a different basin and a general model that represents the whole study area are developed. The verification of the models is made using the discharges at the additionally chosen stations that are not included in the model development. An interface that acquires the drainage area for a certain cross section and estimates the discharge according to the desired regression equation is written using arc objects and visual basic programming language. At the end, regression analysis results of the models are assessed and interpreted.