This paper describes the Alive & Thrive Viet Nam (A&T) project experience in nesting a large-scale project monitoring system into the existing public health information system (e.g. using the system and resources), and in using monitoring data to strengthen service delivery in 15 provinces with A&T franchises. Monitoring data were used to track the progress of the project, make decisions, provide background for a costing study and advocate for the integration of nutrition counselling indicators into the health information system nationwide. With careful attention to the needs of stakeholders at multiple levels, clear data quality assurance measures and strategic feedback mechanisms, it is feasible to monitor the scale-up of nutrition programmes through the existing routine health information system. The following factors made this possible: careful design and testing of forms and reports, training and regular supervision at all levels of the system, quality assurance procedures, feedback mechanisms to the provincial level and below, and clear demonstrations of data use. Although it is not feasible to maintain the entire monitoring system set up by A&T for the franchises, key counselling indicators have been proposed to be integrated into the new monitoring system of the national nutrition target programmes.