A methodology was developed to conduct diagnostic performance assessment and simulation of alternative delivery scenarios in pressurized irrigation distribution networks. It consists of three components, an agro-hydrologic model able to forecast peak water demand hydrographs, a hydraulic model with capability of simulating the network behavior under different flow configurations, and a set of performance indicators for conducting assessments of performance achievements relative to specified targets. As a preliminary work, the current delivery schedule of an existing pressurized irrigation network (system 1) and the resulting effects on crop irrigation management were analyzed by simulating soil water balance and irrigation scheduling at field level. Simulations allowed analyzing the on-farm irrigation management under the current rotation deliveries, and comparing it with an alternative flexible irrigation scheduling to maximize crop yields. Results at field level were up-scaled to the entire command area of the system, showing the usefulness of soil water balance and of irrigation scheduling as analytical tools to demonstrate the inconsistency between the current water delivery and crops’ and farmers’ requirements. This preliminary work also allowed highlighting the need for modernizing the irrigation management in the first of the two study areas considered for the present research work (system 1 located in the province of Taranto, southern Italy). An existing agro-hydrological model conceived to forecast water demand hydrographs in pressurized delivery networks was enhanced through several refinements and amendments of the computation algorithms. The refined model was applied for validation at different management levels on an existing pressurized irrigation system (system 2) located in the province of Foggia, southern Italy, where water withdrawals by farmers and the main hydraulic parameters are recorded on a continuous basis for monitoring purposes. Results from validation showed that the model is capable of forecasting with good accuracy the timing of peak-demand periods, the seasonal demand irrigation volumes, as well as the hydrographs of hourly flow rates demanded by farmers during these peak periods, especially when it is applied to large multi-cropped command areas. Performance indicators, originally conceived for diagnostic assessment in canal systems, were modified for application to pressurized distribution networks, and reference standard values were proposed. These indicators were then applied for validation to the second study area (irrigation system 2), where records of water deliveries are available, and showed their usefulness for diagnostic performance assessments.