Results from application of the IAWQ Activated Sludge Model No. 1, either with or without the excess biological phosphorus removal model of Dold, to thirteen full-scale wastewater treatment plants are presented. For nitrogen removal applications the model is capable of accurately predicting full-scale plant performance and trends in performance, even using model default parameters. Additional work is needed to allow accurate predictions of the effect of reactor configuration and oxygen transfer systems on plant performance. The model of Dold accurately characterized the steady-state performance of biological nitrogen and phosphorus removal systems, but not their dynamic behavior. Detailed wastewater characterization is necessary to allow accurate prediction of the steady-state performance of biological phosphorus removal systems. Further work is necessary to demonstrate its applicability to dynamic applications.