An extended version of the Muskingum flood routing model is developed for application to river systems where multiple tributaries, gaged at upstream stations, unite to a single channel downstream. The Muskingum storage equation is redefined to include the tributary flows as independent inflows to the channel system by increasing the number of x parameters. The routing equation is accordingly modified to contain tributary flows as individual inflows through an increased number of coefficients. An efficient method of analysis is presented which yields direct estimates of the routing coefficients. The model automatically takes into account any effect of ungaged tributary flows and/or lateral inflow in the prediction of outflow. Application of the model, using the method of analysis presented, has been demonstrated on the Meghna river system in Bangladesh, in both real time forecasting and reconstruction modes. The results thus obtained are encouraging. ¿ American Geophysical Union 1993